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?
Even with a custom flatbed, it's pretty hard to keep it as low as a pickup. Look at the profile of the frames in the upfitters manual and you will see why. The CC frame usually has flat rails with no hump over the axle. The crosswise structure has to fit on top of that. The pickup frame has a hump over the axle, and the rails are lower elsewhere. The pickup bed has almost no structure in the area of the hump to keep it as low as possible.