I know of an actual case of a Winnebago that sold new and was determined to be too heavy for the chasis. The dealer gave them the runaround, It was headed to court and Winnebago stepped up and took it back and furnished a new coach of their choosing. Because they went through so much hell to get it done they chose the top of the line Chieftain with every option available and got it.
Jon is right this overloading is serious business. Snap something under there and buy a bridge abutment.