All F-450 trucks are DRW. If you order a chassis cab then you will get the 19.5" wheels and much larger brakes. Don't get stuck on rotor size alone....caliper size and pad area are major factors. You can also order an additional midship tank with the chassis cab models for a very reasonable price.

It sounds to me like you should be looking at the chassis cab models since you can option it exactly like you want. If you purchase an aluminum hauler bed then you will save a lot of weight on the rear springs. You will need an air ride hitch at a minimum because the springs alone in a medium duty truck are too harsh for your fifth wheel pin box. Another option is an air ride pin box or even a Kelderman type rear suspension on the truck.

The current F-450 pickup trucks are really a F-350 Tow Boss package...it is not the same as a chassis cab truck. Try not to get caught up with the HP/TQ ratings between the two models....they are measured in a completely different way with different duty cycles. The F-450 chassis cab will handle that trailer with ease. Happy towing with whatever you choose.