Originally Posted by Mikendebbie
Trying to understand what you want to do...below is a random pic I googled for the rear of a Montana. Is my sketch correctly showing what you want to do?
Hopefully others will chime in with ideas - but this sounds like a bad idea to me.
Your eyebolts would have to be anchored thru studs/structure, with big washers on the inside wall and the outer skin. It seems to me that you will be adding moment forces to the back wall that it was not designed to resist...not to mention inviting leaks and cracking the fiberglass cap. My knowledge of structural engineering and moments has just been exhausted! It just sounds like a bad idea to me - unless my sketch is wrong. Seems like you need to figure out a way to resist the rear end sway by bracing back to the frame (keep the bracing horizontal and low down at the frame level)
I agree with your "moment" concerns - we watched two kid bikes failing around on a travel trailer's rear rack, and then swerved when the rack broke off and the two bikes got squashed like bugs with the following traffic. Our concern led us to a firm in Montreal that made racks that bolted onto the pin
box, using the original pin box bolts (at least Grade 6 !), with some flame cut mild steel "ears" projecting forward. Across those two ears were mounted some aluminum gutter-type channel in which sat the bikes. The carrier also had a backstop to which the bikes were secured and locked. I was able to stand in the truck box and take the bikes on and off the rack. The DW watched the bikes in the rear view mirror. One big advantage of this set up was the limited moment in the pin box area - basically the G force at the pin was the same as that generated on the bike rack.
We have since seen a few more pin box mounted bike racks, mostly DYI, and they seem to work very well. My recommendation would be to bolt
the rack to the pin box, avoiding welding it onto the pin box, unless it is fabricated and welded by a qualified shop.
BTW, I agree that any thoughts of attaching anything to the rear cap is just a large repair waiting to show up. The instantaneous loads on the straps and fasteners could be large, and eventually would no doubt pull off chunks of fiberglass after creating lots of tiny stress cracks in the gel coat.