garry1p wrote:
I think the majority of stress comes from the constant bouncing and jarring depending on road condition.
I have no idea how they come up with the 3500 weight limit but I am sure they would be conservative to protect themselves.
There is also the well known feature of most non-diesel motorhomes that the chassis doesn't usually extend to the rear of the unit. As is the case with the O.P.'s 1992 Winnebago Brave 27 footer, the hitch is mounted to what amounts to the "house" frame, usually not considered sufficient to tolerate more than maximum class II towing capacity of 3500 pounds.
Though some might be fooled by the OEM 2" receiver opening, class II is the hitch specified/supplied by Winnebago for this unit.
Link to brochure that says so. That brochure also contains an illustration of the chassis/frame components themselves, so it's easy to see where the chassis ends and house-framing-only begins.