Personally, I would not try to pull that much with the mini-vans....Been the route of small and undersized tow vehicels and trailers at or near the vehicles limits....not worth the effort...Stick with the pop up or wait until you can get a larger tow vehicle.
Amateur Radio Operator.
2012 Cameo 37RSQ, toted with a 2012, F350, 6.7L PSD, Crewcab, dually. 3.73 axle, Full Time RVer.
Travel with a miniature schnauzer, a standard schnauzer and a Timneh African Gray parrot
I have a similar vehicle, a 2003 Honda Odyssey. Same size, same engine displacement, same number of gears. We've towed extensively our 2,700# loaded Coleman Sun Valley popup (12 foot box) and think it is THE ideal combo. (properly setup with wdh, electric brakes and good balance, of course)
Can you tow a larger trailer? Sure. Will your Sienna still have its original transmission like my Odyssey does at 150,000 miles? Nobody knows, but probably not. Pushing all that air on a full height RV takes a lot of extra push. That translates into a lot of extra heat in the engine bay. Heat kills transmissions, especially.
Our Odyssey lacks a lockout for just D5. I am forced to choose between D5 or D3. That sucks for towing and is a limitation you are not saddled with on the Sienna. You might be fine towing a highwall popup in D4, but I'd shower the van with perfect preventive maintenance (synthetic oil, and synthetic ATF changed at severe service intervals).
Our combo gets 18-20 mpg on the freeway at 70mph. The range is so big because wind makes so much difference! That's only a 5-7 mpg drop from my non-towing mpgs, so I think I've still got adequate safety margin to my vehicle's limits.
Are you equipped with a towing package? Transmission cooler and oversized radiator? If not then scrap the idea.
SweetLou asked if you have the tow package installed on the Sienna. That is a pertinent question. My Town & Country minivan is advertised as having a 3800 pound tow limit, but if you read the fine print in the manual it is 3800 pounds only with the tow package installed. Without the tow package, it is 1800 pounds. That is a 2000 pound difference. If you don't have the tow package installed, your tow limits may be far below what you think they are.
Bobbo, Linda and the furry kids (1&1/2 German Shepherds)
2007 Winnebago Outlook WF331C on a Ford E450 Super Duty Chassis
2010 Subaru Forester w/BlueOx baseplate & Ready Brute Elite towbar
Here's the first rule of minivan towing, don't ask pickup and SUV owners anything about it and expect a decent, knowledgeable answer.
The Sienna is one of my favorite minivans for towing, and another example of a grossly under-appreciated vehicle. Toyota rates the van for 3500 towing IN ADDITION to an almost full van full of people and gear. The guys with pickups and SUVs are used to their tow ratings being grossly exaggerated and overly-marketed, and apply that same thinking to other vehicles even when it isn't true. Truth is, none of them know the first thing about the Sienna van, it's towing abilities, or for that matter it's basic construction.
Suffice to say, there ARE bigger trailers you can tow, and the 3500 tow rating is not really a consideration once you are outside the warranty. It's nothing more than a statement about what Toyota was willing to stand behind when the van was new. Once they stopped paying for repairs, what you do with your van is nobody's business but yours. There are NO legal reasons to concern yourself with tow rating, it is NOT a legal limit.
Now, all that said, you do have some liabilities with the current van. Your's being a 2006 model means it has the weaker 215HP/222Tq 3.3 motor rather than the newer 266/HP/245Tq powerhouse the current models have. Point is, a newer van will be able to tow more than yours. You still have a very robust van, with a solid 5-speed transmission, great handling and brakes, a decent wheelbase to rear overhang ratio, and a low center of gravity. A Trailer behind a Sienna will be in much better control than it would behind many higher-rated vehicles such as most mid-size SUVs.
My recommendation, as someone who tows with a slightly LESS powerful, but otherwise very similar van as yours, is to try and find an aerodynamic trailer (sloped front, rounded corners, full belly-pans...etc.) with a good suspension and brakes, low center of gravity. Something like an Airstream or an Award would be a good place to start. Don't worry about the weight as much as the drag, because once you are at highway speed it's drag that puts the majority of load on the van. A 4000 pound Award will tow easier than a 2000 brick-shaped conventional trailer. Have your van fitted with an appropriate class III hitch (aftermarket ones rated up to 5000 pounds are available right off the shelf from Reese and others. If the fact that custom-fit-5000-pound-rated-aftermarket hitches are available for a van who's tow rating never exceeded 3500 pounds doesn't make a statement, it should.) and get it wired for a 7-pin RV plug and a high-quality electric brake controller if it isn't already for your popup. Then when you go looking for trailers you can hopefully talk the salesman into a "test-tow" before making any commitments. Most will happily oblige if a sale is on the line. You will eventually need a Weight Distributing hitch setup with 550 or 600 pound bars and some form of sway control. You might want to have this equipment available before asking for a test-tow as well.
Again, as someone who already does what you are looking to do, and with less van I might add, I think you are going to be surprised.
'11 Ford Expedition XL 5.4L (Primary tow vehicle)
'04 Mercury Grand Marquis 4.6L (Backup tow vehicle
'04 Ford Freestar SES 3.9L (another Backup tow vehicle)
'97 Lincoln Mark VIII 32v 4.6L (another Backup tow vehicle)
I have a 2000 Odyssey and won't tow much with it. Known weakness is the automatic.
Even the new body style (2006 on), which has a better tranny, but still the weak
Brother also has a 2000 Odyssey and he's going in for his 3rd tranny rebuild soon
Doesn't tow, but hauls seven adults and tons of cargo when we go camping. That
roof rack cargo container is aero designed, but still increased frontal like towing.
Mechanic is a Master ASE who used to work, manage service departments at Toyota
and Honda, now owns his own shop. Says the Toyota auto better, but still he
would not tow with it. Especially at the limits (he and I agree on how it's
supposed to be calculated).
Make sure your Siena has the tow package (external ATF cooler).
Just make sure you follow your glove box manual towing section. Go
out and weight your setup axle by axle both empty and fully loaded.
Then do the simple math based on the glove box manual info. A 'dry'
2,800 lb trailer will most likely much more.
Here is the hot link to a post where my towing info from the glove box manual
Notice that if my Odyssey is loaded up with 7 adults, it has a MTWR
of 850 lbs. I assume that the cargo also plays, but it doesn't mention
that. If only 2 adults, then the MTWR is 3,500 lbs.
-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...
I have a 2000 Odyssey and won't tow much with it. Known weakness is the automatic.
Thanks for all that Honda information Ben. Too bad the OP is asking about a Sienna van, which Toyota rates completely differently. There's a reason why Honda's are not among my favorite minivans for towing, and some of the info you posted explains why.
I towed with my minivan all over the US east of the Mississippi for almost 100,000 miles. Never blew a transmission or anything else. My only complaint was the stupid "run flat" tires that wore quickly and had terrible traction when it was wet.
I have a 5.7L Tundra now but still miss the MPG with the old minivan.
27 foot TrailManor 2720 pulled by a Toyota Tundra (381 HP 401 TQ) - Dual EU2000i Honda Generators