I got the spray in liner from ford put a rough country rubber mat in as well, also got the tailgate cover from ford accessories. I like the rubber mat easy to take out wash and put back in, it has little dimples on the bottom for airflow I guess. Cover the box with a truxedo x15 tonneau rollup...
Here is the naiper air mattress 42" wide, a bit of a gap along the edge, mind you this is without the tent. The built in pump is kind of joke unless you want to spend most of camping trip blowing up the mattress. The tent does fit over the rollup tonneau cover.
No it doesn't have wheel cuts outs, but the size it should fit snuggly between them. We tried using two separate air mattresses and it didn't work so well, made for uncomfortable sleeping.