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Open Roads Forum  >  Truck Campers

 > Frame Stiffing to reduce Porpoising?

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Posted: 01/27/23 06:49am Link  |  Quote  |  Print  |  Notify Moderator

mkirsch wrote:

I'm betting facebook guy thought nothing of his 2" of flex too...

I have to wonder about box frames. For 1 thing, C channel is used in heavy trucks. If the C can't be stiff enough, and fit in required space, double the C.
Plus, if need to add a bracket to mount something, drill thru the vertical part, use bolt to fill hole, and torque tight with nut and flat washer. Loose very little strength unless big hole.
Box section, drill and tap. But you can only get threads for the thickness of 1 side of box. A bolt thru hole drilled in both sides, then nut on other side, can distort both sides, and both flanges. This would weaken the frame a bunch.

Grit dog

Black Diamond, WA

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Posted: 01/27/23 09:13am Link  |  Quote  |  Print  |  Notify Moderator

FB guy is/was overloaded a similar amount as you are currently. Possibly less overloaded if your unknown camper weight is 5klbs. Based on gvwr of both trucks.
Heavier camper? Yup for sure. Far more stout of a truck? Yup for sure.
There’s always 3 sides to every story and I would 100% believe that truck got to experience some extreme dynamic loadings.
Human nature is to defend one’s own position. And “forget” that little “episode” when the camper got airborne over an unexpected bump….or 3.
The difference between driving to Alaska and driving in Mehico compared to 99% of the roads in the L48 IS real.
Despite best efforts, when we drove to AK and around AK a whole summer I hit countless major frost heaves, where I was surprised the truck was still in one piece and the camper wasn’t laying in the road behind it.
Compare that to 1000s of miles in or between the Cascades, Rockies and Midwest, those types of things were and are MUCH less prevalent here in the contiguous US of A.
You could likely go another 10 or 100 years and the truck frame will be just fine, or you could come around a corner and the road settled due to a landslide and hit it and the whole thing fold like a tortilla.
That said, you’ll be hard pressed to find anyone to box or flitch plate the frame that isn’t just a backyard fabricator who doesn’t care about having a $3M corporate liability umbrella. Any shop with real sense about liability protection will either laugh or politely refuse the work short of doing anything that isn’t on a stamped plan/calculations. Period.
And there ain’t many places with mechanical engineers on retainer to do this. That’s the other side of this.
Find someone to cob up what you think you want? Sure.
Have the design calcs to back what is done? Nope.
Maybe 30-40 years ago. Not now.
-Someone who gets structural engineering designed regularly and has seen a decided shift in how “everyone” looks at liability.
25 years ago, no one had an issue with me designing a formwork or scaffolding or false work system even though I was a new engineer/Supt and didn’t and still don’t have my PE.
Now, on most public works projects, you literally can’t do anything that supports any live load or construction load without a stamped design.
Different industry, exact same principles. Exact.

Nevermind all the previous discussion about ROI which is also way in the red.

This is one of those, time to find a new thing to use as a brain teaser.

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Posted: 01/27/23 10:44am Link  |  Quote  |  Print  |  Notify Moderator

I carry a heavy camper and tow a heavy trailer. Whether it was my F250 with an AF811 or my current 5500 with Mammoth, I look at keeping loaded front axle weight the same or more than when it is unloaded. This may mean loading the camper or truck differently or adjusting my WDH so tongue weight does not lighten the front truck axle. Keeping your load in the proper horizontal CG not only reduces stress on the frame but also helps overall handling of the vehicle.

Reading through this thread, I am not convinced that there is anything wrong with the current truck frame. You want to make sure your axle weights are within limits and the front end is not unloading due to too much weight rear of the axle. The camper should be sitting level in the truck and may need shims in the front or back if the bed crowns in the center. If you are seeing excessive bed movement, perhaps the bed is coming apart and you should look underneath for visible signs of cracking or corrosion. The camper should be evenly anchored at 4 points - With FastGuns or other quick release levers, it is fairly easy to verify tension is the same on all of them. Having uneven tension on the camper tie downs may be good when you are moving slowly on uneven terrain to relieve stress, but not on highways.

I had the adjustable Rancho shocks on my F250. Since the front axle weight really was not changing much from unloaded to loaded, the shocks stayed at mid-level damping. The rear axle was the one that varied greatly (in my case from 2750 lbs to 8000 lbs) and this is where adjusting damping between minimum and maximum gave me the best unloaded and load ride.

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Posted: 01/29/23 08:49am Link  |  Quote  |  Print  |  Notify Moderator

X2 on grit dogs take on the liability of a competent shop to do any frame mods. Anyone managing a successful shop will realize that not staying in your swim lane can have serious consequences. In my 40 years of employment with the largest super major oil company, any modification to any process stream had to go before the management of change committee. Six Process Engineers playing the "what if" game. You learn pretty quick to not go cowboy off on your own. So bottom line, if you can find somebody to weld on the frame, you don't want them.
OP: are you sure you're not just seeing the camper rock back and forth, the spring loaded Fastguns doing their job?
Regarding camper weight..The first time I loaded my Bigfoot on my then 2016 Ram 3500 SRW and weighed it, I was draining water out of the tank.

* This post was edited 01/29/23 09:31am by TxGearhead *

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Posted: 01/29/23 10:49am Link  |  Quote  |  Print  |  Notify Moderator

I get concerned about our camper porpoising sometimes as well. It looks like the cabover is moving a ton when I look up and out the windshield. But in reality, it can't be moving too much or it would be hitting the sharkfin antenna. And, since ours is sitting on a rubber mat in the bed of the truck, and the center of gravity is right on the rear axle, the flex in the rubber mat probably accounts for a lot of the movement. As mbloof said, 2" of movement at the front of the cabover isn't very much movement at the front and back of the truck bed.

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Grit dog

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Posted: 01/29/23 01:46pm Link  |  Quote  |  Print  |  Notify Moderator

OP is, or was, asserting his truck frame is flexing 2”[emoticon] Not just the camper overhang.
But then he revised his assessment to 1”. Which is also not likely. At least not as a general matter of course driving down the highway even on concrete.


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Posted: 01/29/23 02:05pm Link  |  Quote  |  Print  |  Notify Moderator

F450-F550 would be the method to strengthen the frame.

Otherwise post the scale weights, door sticker and a video of the frame in motion.

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Posted: 01/29/23 03:59pm Link  |  Quote  |  Print  |  Notify Moderator

TxGearhead wrote:

OP: are you sure you're not just seeing the camper rock back and forth, the spring loaded Fastguns doing their job?

I always get a kick out of these sorts of comments. [emoticon]

So a flat hard object sitting flat on another flat hard object is "rocking"??!?!??! hahahahahahahaha

Turnbuckles have springs in them because the frame can flex and twist while the truck is going down the road and without the springs the attachment points on the camper could get torn out.

- Mark0.



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Posted: 01/29/23 06:07pm Link  |  Quote  |  Print  |  Notify Moderator

Executive Summary:

Not enough facts were provided by Adamis, despite multiple requests from RV.net members willing to offer their experience and advise.

Available Facts:

From First Post:

adamis wrote:

I have a 1999 F350 Dually Quad Cab Long Bed. My camper is the Bigfoot 2500 and with everything loaded up is probably in the 4500lb to 5000lb range.

From Signature Photo:

Clarifies CREW Cab (not "Quad Cab," which is the Ram equivalent to 4 door Extended or Super Cab) Confirmation of Crew cab is important for looking up the correct vehicle references in the 1999 Model Year Consumer Information for Truck Camper Loading for Ford Pickup Trucks.

From Second Post:
adamis wrote:

my truck is only two wheel drive. Fine for California

From Third Post:
adamis wrote:

the reason I picked a 7.3 is the smog equipment is non existent. and I'm still legal in California. I also have close to $10k in "goodies" in this engine Larger KC Turbo, Larger Injectors, Chipped,

By definition, the "larger KC Turbo, larger injectors, chipped" each individually and in combination means that the statement "I'm still legal in California" is false, and not at all a fact.

From Fourth Post:

adamis wrote:

It took me a while to find it but Max Payload for the Crew Cab Dually Long Bed 2x4 appears to be 5355 lbs and the 4x4 is 4910lbs. My camper according to the tag on it weighed 2906 and that included 50 gallons of water and 20lbs of propane. Going to a 4x4 conversion that would leave me 2000lbs for people and gear which would be way more than we would ever carry.

Questions on Maximum Payload Capacity assumptions:

From What resource did you obtain the "5,355 lbs" Maximum Payload Capacity for CREW CAB DUALLY LONG BED 4x2?

Did you account for the different Max Payload that applies to the 7.3L diesel?

Did you account for the different Max Payload that applies to California?

Did you account for the different Max Payload that applies to Model Year?

Did you account for the options that you specific truck was built with?

More Accurate Information to Consider:

It remains unknown what options your truck was built with, the weights of which reduce the maximum payload capacity of your your specific truck. Likewise, the weights of the $10K in goodies that you added is also not known.

However, given that it is well established that your truck has the 7.3L diesel, and that are in California, and therefore probable that your truck was built for California, with an 11,000 lbs GVWR... the Maximum Payload capacity for a 7.3L diesel equipped F-350 Super Duty Crew Cab 4x2 172.4" wheelbase (long bed) dual rear wheel pickup is 4410 lbs, before factory options are subtracted.

Source: 1999 Ford Source Book, Super Duty F-Series Page 86 (Dealership Hard Copy Print)

Questions on Big Foot 2500 Camper Weight determination:

How did your camper weight drop from 4,500 to 5,000 lbs down to 2,906 lbs?

Have you actually weighed your camper?

Have you actually weighed your truck?

As other rv.net members have pointed out, getting physical weights is step 1.

There is no point in guessing at what you can readily determine with certainty.

The Ford Pickup Trucks 1999 Model Year Consumer Information Truck Camper Loading guide sets forth the Minimum Requirements and Maximum Weights of truck campers on 1999 Ford Pickups.

1. The 1999 F-350 Super Duty Crew Cab DRW 172.4" WB 4x2 is only recommended for hauling truck campers if the truck is equiped with the optional CAMPER PACKAGE 532.

The CAMPER PACKAGE 532 consists of the following equipment for 7.3L diesel 4x2 applications:

A. Front Stabilizer Bar
B. Rear Stabilizer Bar
C. Auxiliary Rear Springs
D. Slide In Camper Certification

Question: Does your truck have the foregoing optional equipment A-D?

2. Factory Option Weight distribution between Front and Rear Axles for
Base 1999 F-350 4x2 Crew Cab 172.4" Wheelbase DRW 11,000 lbs GVWR

Example of Assumed Front Axle additions/subtractions:

7.3L Diesel w/4R100 Automatic: + 604 lbs.
California Emissions: + 2 lbs.
Front Stabilizer Bar: + 34 lbs.
Rear Stabilizer Bar: + 2 lbs.
Auxiliary Rear Springs: + 1 lb.
Lariat Trim: + 19 lbs.
Aluminum Wheels (-22 lbs.)
Running Boards: + 46 lbs.
Air Conditioning: + 44 lbs.
Power Windows/Locks: + 3 lbs.
40/20/40 w/Power Driver seat: + 32 lbs.
Trailer Tow Mirrors Electric: + 8 lbs.
Chrome Front Bumper: + 7 lbs.
Chrome/Painted Rear Bumper: (-17 lbs.)
LT235/85R16E A/T Tires: + 26 lbs.
LT235/85R16E A/T Spare Tire: (-11 lbs.)
AM/FM Stereo CD Player: + 8 lbs.
Trailer Tow Hitch: (-11 lbs.)

Subtotal of Example Option Weight on Front Axle: 775 lbs.

Example of Assumed Rear Axle additions/subtractions:

7.3L Diesel w/4R100 Automatic: 98 lbs.
California Emissions: 1 lbs.
Front Stabilizer Bar: (-3 lbs.)
Rear Stabilizer Bar: + 26 lbs.
Auxiliary Rear Springs: + 32 lbs.
Lariat Trim: + 20 lbs.
Aluminum Wheels: (-22 lbs.)
Running Boards: + 29 lbs.
Air Conditioning: (-3 lbs.)
Power Windows/Locks: + 3 lbs.
40/20/40 w/Power Driver seat: + 21 lbs.
Trailer Tow Mirrors Electric: + 3 lbs.
Chrome Front Bumper: (-1 lbs.)
Chrome/Painted Rear Bumper: + 80 lbs.
LT235/85R16E A/T Tires: + 51 lbs.
LT235/85R16E A/T Spare Tire: + 101 lbs.
AM/FM Stereo CD Player: + 2 lbs
Trailer Tow Hitch: + 60 lbs.

Subtotal of Example Option Weight on Rear Axle: 478 lbs.

Based on the foregoing examples of option weights, the actual cargo carrying capacity for the vehicle as equipped is in the range of 2,961 lbs., as determined on Page 43 of Ford Customer Service Publication FCS-12177-99.

The longitudinal center of gravity zone is 60.2" forward of the tailgate at the front edge of the longitudinal CG zone, to 44.7" forward from the tailgate at the aft edge of the longitudinal CG zone.

Obviously, the manner in which your specific truck is equipped may vary from the above example factory options selected for demonstration purposes.

Equally obvious is the fact that your truck does not have 5355 lbs of cargo capacity, or net carrying capacity, as you previously have cited.

It is suggested to review how the truck is engineered, before trying to re-engineer it.

The first and most basic step is to weight the truck without the camper, and then weigh the truck with the camper. With each weight, weigh the front and rear axle on separate platforms. This base line data is foundational to any future decision on how to manage camper weight on your truck within the original design limitations. The Federal Certification Label on the door jamb and the Slide In Camper Certification (if equipped) are also essential GAWR and GVWR data sources to compare your actual weights with.


No paticular place.

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Posted: 01/29/23 06:21pm Link  |  Quote  |  Print  |  Notify Moderator

BigToe wrote:

Executive Summary:


Excellent breakdown of the subject but I'm betting the OP just keeps insisting that it's OK because he wants confirmation, not an actual answer because it's most likely not the answer he will ike.

Tammy & Mike
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