Kohldad, did you attach the frame to the camper? If so how? I need to do something like you did.
Did not attach it to the bottom. I cut the foam board in half so easier to store. The foam goes in the camper, the boards lay beneath when I take it off the truck. In the last 5 years we've done 66 trips and probably loaded/unloaded the camper 62 times because of our HOA.
I wouldn't want to attach it to the bottom as each screw hole you put in would be a place that moisture could be sucked up. You could attache it with some caulking though since there isn't much force on the wood or foam.
