Take your rig to a custom hitch builder and get his opinion after looking at the undercarriage. Many bumpers are simple add-ons without support to the true "frame". Extensions for the coach are often smaller than the chassis frame. My Chevy frame is a unibody and not real strong the custom hitch I added tied the frame with the extensions and the bumper, it still will only handle about 750 pounds weight, but pulls over 7500lbs. Think of the five pound weight held in your hand tight to your body and then extend your arm out. Heavier? No, but dynamically you are pushing the connection a lot more.(That may be a weak analogy, hope you get the point). The farther you extend out from the main frame, the less weight you can carry. It also could beat your frame to death.