I am thinking about getting a regular cab F-350 dually and 208" wheelbase. Then install a long sleeper cab from a over the road truck, and make it into some sort of camper, and still able to tow a large fifth wheel! It would be a 92" stretched Super Mega Cab! With captains chairs for at least 6 and a wheelchair lift and room for at least 2 wheelchairs too! I am still on the sidelines about a tiny bathroom or not? Perhaps just a sink and small hot water heater or heat exchanger from engine heat to warm the water.
And then install a 6' long (or so) bed on the back, with minimal overhang from rear axle to bumper. This way I can mount the fifth wheel hitch at least 2" in front of the rear axle, and still have clearance between the fifth wheel and bumper. . . .
Fred.