Exactly.  I own a Lance and I agree, they are all barges.  Drummers (RV salesmen) will tell you anything to make a sale.  Keep in mind that once it's on your truck...it's yours along with the payment book, not their issue and finally..

You can modify about any suspension to carry about any weight and look 'good', but like Nobody says, the components you cannot see, spindles, bearings, differential gears, brakes, driveline and transmission are all overloaded and can fail much sooner than if not overloaded.

Then there is emergency stopping, evasive maneuver issue.  Being over capacity adversely impacts stopping distance and handling.  Nothing better than stabbing the brakes in an emergency situation and eating the rear end of the vehicle in front of you or running over a pedestrian because you cannot stop.

All things to consider...serious things to consider.