The camper should not rest on the sides , only the floor . Be sure that the foldable sides are less height than the distance from the truck bed to the underside of the camper wings . I used 4 short Torklift anchor guards for tie downs . They attach to 1/2” D rings bolted to the flatbed . My flatbed is diamond plate aluminum and the camper sticks like glue . If yours is smooth you will need a rubber mat under camper so it doesn’t slide around . I would also recommend side stops to prevent side movement . There are several good discussion in TCU of campers on a flatbed , worth you time . Good luck
