This is how I would campout when fishing at Port A. Fishing rods went in one leftside of the box, and chairs, rod holders, and other gear went in the rightside. Air or foam mat went on the box, keeping us off the truckbed ribs. 1" stick-on foam window insulation can be used to fill in the gap between the tailgate and bed, to keep mosquitos out.
Before I build the box, we used (5)1x6 boards, cut to the width of the bed, place on the lip below the window to use as a bed at the front of the camper.