I've had some conversation with Jay on this in the past. Keep in mind he's bolting all sorts of things into the frame. Rivets galore and if I'm not mistaken, those massive hinges on the barn doors are Rivuts with bolts and are really strong -- I watched him hang on a barn door the first time I visited his shop, and that's a leveraged weight. I think he's also using the same grey 3M caulk/adhesive under those as elsewhere in his builds (he said it was 3M 540).
I put up my Wave3 heater on a light angle alu frame attached to the camper frame with 4 alu Rivuts. The assembly weighs ~10 lbs and has bounced all over creation with no loosening or pull.
On post #2 here, I you can see how I set up the 8020 frame on my barn door to hold a Rotopax. Thats made with two pieces of 8020 with just the skin sandwiched between. Both pieces of 8020 are VHB'd to the skin and there's two through bolts on each upright. I hung up a full 3 gal Rotopax and additional support I made for the Rotopax (26lbs total) and took that on some really rough trails with no drama. I also had a 10 lb kitchen roll up hanging on the inside and a full Trasharoo on the same mount for around 50lbs total.
I put up the awning channel you can see here with VHB on the skin with self tapping screws(caulked) into the frame and a bead of that 3M 540 when I first got the camper. I'll never get it off.
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The one thing that HAS failed for me was this:
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I used VHB on the base half piece of 8020 to the skin and two self tapping screws through the skin and into the frame. Held for a while, but started to loosen when it got a got knock on the extended swing out arm. Started to loosen the self tapping screws out due to the overly small surface area for the VHB not giving enough lateral support. My fault, bad design cause I was using an available pre-drilled scrap piece. This one on the other side, which used a longer piece of 8020 as the mounting base took some equally hard knocks and was fine.
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I made a new double length base for the damaged one, drilled out the existing holes and added a third for Rivnuts and it's like a rock now with VHB and 3 Rivnuts. I also coated the Rivnuts with epoxy putty before installing them for good measure.
My takeaways are that you can hang some pretty heavy weight on the camper skin/frame combination without through drilling the frame. I think the key is both a mechanical faster into the frame (Rivnuts and bolts for anything heavy) along with either VHB or a permanent sealer/adhesive (eg, 3M 5200, 3M 540, or Sikiflex). It's pretty similar to woodworking where glued and screwed will always hold better than either alone if the joint is made right. My guess is we'd do more damage through bolting clear through the frame. I would think the clamping force might cause more metal fatigue. Also, the loads are almost always going to be shear forces, not tensile or straight pull. Also, the more square inches you have for mounting the better, especially with VHB or adhesive. Be sure to liberally coat the screws or bolt heads with a sealer too, of course.
Keep in mind, that when Jay was using 8020 for the pull out bed rails, these were mounted onto the frame surface with bolts and, I assume, Rivnuts. I don't think he even used VHB on these, but they're bolted every 8 to 10 inches. They are like a rock and are holding over 300lbs in the case of me and my wife.
Edit: one other example I just thought of is the awning mount Jay fabbed for my 23 Zero. That weighs about 45lbs and is held with four bolts into the frame and the 3M 540 and definitely not through bolted. Again, no problems and it bounces around back there on rough trails more than anything.
Hope this helps!