2015 Lance 1172 Too Shallow for 2015 Chevy 3500HD Bed

The mats I got are very high density but the camper does seem to be able to move more than I would expect. I was hoping that perhaps a more sturdy turnbuckle would help. The turnbuckle that popped loose didn't loosen, it simply detached at the top due to the amount of movement when I hit the bump.