That chassis, as it came from Ford, was rated 20,000 pounds GCWR and given a nominal tow rating of 5000 pounds. Used bare (i.e. with a toolbox and fifth wheel and "bumper" hitches it was regularly used as a tow vehicle for RV delivery, up to about 14,000 pounds on the fivers.
But a motorhome manufacturer changes things, extending the frame several feet behind the rear axle, sometimes also stretching between the cab and rear axle, and building a house that uses up most of the weight carrying capacity that would carry your tongue loads.
It is unlikely that the hitch receiver, and the frame extensions to which it is mounted, are up to the 700-900 pound tongue loads of a 5000 pound trailer. The hitch itself might be rated to pull 5000 pounds, but effectively that is a flat tow. There used to be dollies, like the tow dolly for a car, that you could use to carry the tongue or hitch weight of a trailer. I have not seen those since the 1960s.
The hitches on a finished type C motorhome are usually marked with warnings against using weight distribution. With the hitch receiver 8 to 14 feet behind the rear axle, the geometry is all wrong for the assumptions used to design and rate WD hitches. A hitch design that carries the trailer tongue weight all the way forward to the rear axle might work. We used one of those (a DrawTite axle hitch) in the early 1960s but I have not seen those since, either. It was something like a super-strength WD hitch longer than the tow vehicle overhang.
Tom Test
Itasca Spirit 29B
