Fixing the front of the truck bed wall. Picture links fixed.

It appears that your camper slid because it is riding on that piece of plywood. I have a 4800+ lb. Arctic Fox and it doesn't budge because it sits on a rubber bed mat. I did however put a true 2X6" piece of solid ash across in front of the truck bed to help prevent the camper from riding against the thin headboard used in the trucks now days. The 2X6" helps to spread the load out across the bed of the truck.