But .... Ford has no idea what length of Class C the manufacturer is going to build on any individual E350/E450 cutaway chassis for any particular E350/E450 wheelbase ordered.
The E450 158 inch wheelbase Ford chassis under our 24 foot Class C handles perfectly - nothing wrong. Winnebago either lucked out since our motorhome was a short one, or paid attention to what they were doing.
Class C manufacturers need to carefully(?) design/engineer both how much they extend the rear of the E350/E450 frames, and how much weight is winding up on the rear axle versus the front suspension.
It seems to me that the bulk of the responsibility might be tilted towards the Class C manufacturer when using Ford's (or Chevy's) cutaway van chassis as a starting point.