Closed cell Foam on Bed

I tried foam before on a long trip. When I got back my clearance was greatly reduced by the foam squishing down. I think the best way to go is just build a wooden riser the height you need.

i've got a rubber bed mat with insulation on top of it. it has absolutely not compressed the insulation at all. i was impressed. no sliding. been on rough roads, high speeds, high winds, no issues. i'd be concerned about slippage if it's insulation directly on the bed but i like the support and the insulation it offers over just an outer frame of 2x2's or the like.

Thanks for all the replies so far , would still appreciate any more . I actually need about 3 inches to have clearance of the camper over hang to top of cab . I have bought 2 sheets of 2" , 4x8 foam insulation . I too have fiver hitch rails to deal with . I was thinking about setting the foam sheets in the floor of the bed box ( tail gate down, 6.5' box) and then letting the camper down on top of the sheets . On the bottom of the camper there are 4 rails which run across the outside floor that may groove into the sheets. I also feel that the fiver rails may groove into the bottom sheet . Do you think this will prevent the sliding or not?I am not off roading at all. Open to all suggestions and previous experiences. Thanks

Single sheet of plywood. Get a 4" plumbing hole saw. Cut round "cookies" out of the plywood. Screw the cookies back to the original sheet of plywood between the holes you just cut - each cookie will have a pre-drilled center hole anyway. Gives you the thickness of 2 sheets for the weight of a single sheet. Put it in the bed cookie side down. Bed mat on top - good to go. BTW, I have a 4' x 6' stable mat I use for something else. Hate to move it - weighs in at about 125#!!! ST

I have used the foam before with my previous Lance camper to clear the fifth wheel brackets in my truck. I was initially using plywood with a thin rubber mat but decided to give the foam a try for weight savings and more insulation under the floor. I noticed a little bit of movement fore and aft when driving down the road with the foam. It wasn't much but I could see the nose of the camper moving(bouncing) more than with the plywood. This was with 3/4" foam.
With my current Northern Lite I have built a 2x2 framed plywood floor to space it up. I won't do the foam again. I did like how it weighed next to nothing though.
This is my experience. I believe others have had good success with the foam though.

Stable mats are what I have seen used a lot.

I attached 2 x 2's to the bottom of my TC. Followed the screw pattern on the mbf board there. Never got around to installing foam in between.

Because of my manual jacks and setting each corner down, I was afraid I would crush the foam on the edges. So I made a 1x6 frame and filled the center with 3/4" foam. Works like a champ and only takes a couple minutes to assembly/disassembly. I cut the foam board in half so it fits in the camper when not in use.

Alternative method is to secure the wood to the bottom of the camper