[mhbell]

Looks to me that you have a couple of options.
If a floor for the hitch rails was needed you could always install a piece of Diamond plate steel between the frame rails of the truck. another possibility would be to install a goose neck hitch and pin box. That could be a better option if you are going to install a flat bed. That way the hitch would be hidden when you were not towing. No rails in the flat bed that way and more room for stuff when towing.