Foam Board or Rubber Mat For Under Camper?

I've been hauling a Bigfoot 2500 for 8 years. Started with just a 1" thick 4'x8' bed mat but found that the bumpouts at the rear were contacting the unprotected bed. I could tell because the aforementioned screws on the bottom of the camper were digging into the Line-X liner in these areas. So I cut some pieces of rubber from a thick door mat to fit into these areas and tied them to the rear bed tie down loops. I later added a piece of 1" foam board under the rubber mat and made sure to add foam pieces under the bumpouts too. The camper overhangs the truck bed by about 2' but I've had no problems with the foam/mat ending at the end of the truck bed. I'm sure it's designed to handle the lack of support beyond the truck bed. And that's why it's important to support the bumpout areas at the back as this is the last area of support before the overhang.