Raising camper height...wood/foam/rubber etc...

I second the pink foam sheets from Home Depot. They come in 1/2", 1", and 2" thicknesses and you can cut them with a utility knife. Adds very little weight and adds pototenial insulation and it will conform to the bed of the truck. I have a piece on a plastic bed liner with a rubber truck bed mat on top and then the camper and there is no slippage of the camper.