As discussed on here many times, if you have a drop in bed liner you need to remove it. You want plywood, rubber mat, EVA foam mat or a piece of structural foam (pink or blue stuff from Home Depot) between the camper and the bed. This protects the bed, but more importantly keeps the camper from moving around. Tie downs keep the camper on the truck, but will still let it move around quite a bit in the bed which can damage the truck or the camper. I have used the jigsaw puzzle type stuff with no problems for a few years.