Foam Board or Rubber Mat For Under Camper?

I've used a 3" structural foam board for many years and it had been just fine. Concerning foam: Yes it does compress here and there due to the corrugations in the bed, but that's exactly what you want. On the top side, it also shows indentations from screws and some lap joints (Bigfoot 2500), but again that's exactly what I want it to do. It's has to support less than 1 pound per square inch, and after it's initial conformation, it's supporting the camper equally on every square inch. I need the extra height to clear the cab, so the weight of plywood, boards, and a horse mat was a couple of hundred pounds and a P.I.A to take in and out whenever I wanted to use the truck for "actual work". Foam has been good for me and cheaper as well. I am not sure how foam would act if only an inch thick, though. For a "no rise" situation, I might go for some slats and a thin rubber mat. Plywood is not a good idea in Oregon due to the moisture damage, in my experience.

EDIT: I also cut extra pieces of foam to support the Bigfoot wings. They are light and easy to deal with. Nothing moves.