Which truck / camp rig is taller (to the top of the camper including roof top equipment) and hauling the same camper: 1. F450 Cab and Chassis with a flat bed, or 2. F450 with pickup style box?
Possible to make it same? sure, but the structure of a flatbed is inherently different because of the assumed use, and, as pointed out, a 'bed' gains overall strength through the quarter panels (think unibody). Different beasts.