Started with a camper and the full bed mat. Got a 5er, they cut the bed mat in half across between the wheel wells, and cut slots in each half for the rails. Still have a bit of rail height above mat.
Whenever have to carry 4 x 8 sheets in the truck, use three 8 ft 2x4s to clear the hitch rails
Then got another camper years later. Used the 2 x 4 boards under the camper same as when carrying 4x8 sheets. The camper hold downs keep it all in place. The back of the camper hangs down below the bed so no problem with boards coming out the back with no tail gate there.
