I have a Bounder, and toured the factory a few weeks before buying in 1996. The center of the RV is two supports that go front to back, separated by 14.5" so the center roof vents and A/C units sit between these two supports. The cross pieces connect to the sidewall from these two main supports, where is a great question, it all depends on the year and length of the RV.
This is some pictures of my roof, it's supports, and the Herculiner that I put on it last April.
This is my front pair of panels. 120 watt mounted on a curved roof, 102" wide.
This is the mount it is held on with three rivets into the frame, and then the bottom half is 6" long aluminum, with nutsert in the upper piece, bolt you can not see from the outside edge pointing inward.
This picture shows the bigfoot panel mount sold by RvSolarElectric for $35 a set back in 1994. I wonder what they cost today?
This picture shows the panels tilted while I was working on the roof.
The panel supports are about 6" long, I make them out of 2" angle aluminum from Home Depot. Put them on with lots of rubber roof sealant under it, and over the top of the screws. I used 3 - #10 screws into the 3/8" thick plywood, it is very thin and weak. Basically the rubber roof sealant holds the panels in place. Mine are all installed in 1996 - 1999, and have traveled all over the United States. Now I even have Herculiner over the top of the panel mounts, and they will not go anywhere the motorhome is not going with them.
I used nutserts to hold the panels in place, and you can see the tamper resistant bolt in one picture, you must have the correct adapter to remove that bolt. The nutsert it pop riveted into the panel and will not turn.
Looking at the pictures again, you will notice that the mounts are under the solar panels when possible, more for theft protection than rain avoidance, but still they are protected from direct rain.
See the statellite dish? It is mounted directly over the air conditioner air duct, so I ran a 3/4" hole and it's wiring into the air duct. So when it leaked, all that happened is water started dripping from the A/C duct. I sealed the leak, and that fixed that problem. The 1-1/2" square metal supports that I talked about are near the center of the roof, 14.5" apart, and I think that some of the screws into my solar panels went into those tusses. That is one reason I have the solar panels separated in the front, main reason is getting to the front mounting brackets to tilt them when parked with the windshield pointed north. However I rarely get up on the roof, and do not tilt them anymore, they are tilted to take these pictures because I was applying the Herculiner rubber to the roof.
You can see the metal roof trusses by removing the air conditioner air filter cover, they will be up there someplace! Probably above the air duct. Also in my RV, the air ducts run directly below the center truss that runs the length of the RV.
You might be able to find the truss with magnets. They might roll to where the truss is, then stop. The sidewall, on a cold day, I was able to see the supports by looking at where the dew formed on the RV.
* This post was
edited 04/25/12 09:51pm by Golden_HVAC *
I also have had great success with the 3M VHB tape. However I also used a couple of #10 Stainless steel screws and dicor to cover it all. I also used it to install the winegard dome too. Its available on auction sites in small quanity and various widths.