Plywood & Rubber mat question ( Who's on first )

I tried the foam but it stressed areas of the camper bottom that had weak areas.

Tired of the heavy rubber matt, I cut 3 strips of plywood 1 foot wide and stapled 1 foot wide strips of rubber to the bottom of the plywood. Using stainless staples it's held up and easy light weight to just slide in the three rubber strips of ply into the truck bed. The ply gives even pressure to the camper bottom.