The more I look at it the more I think I'm just going to attach 2x4s at the perimeter of the camper and at the basement walls. I'll use a few screws on each 2x4 to secure it to the "joists" so I can easily remove them if I need to get at the access panels. I'll need to bridge the three supports at the back of the back of the truck bed with a 2x4 since there isn't a single "wall" there. Keeping them attached to the camper will make loading and unloading easier.
Please don’t. There are multiple solutions that are better than what you’re suggesting. Not that it won’t work, it’s just a poor solution to your issue.
Also not advisable for resale. If you were to sell it to anyone who saw and understood that, it would either make them walk away or at least really wonder what other weird jethro engineering was hiding in the camper.
Yikes.
