Pull the bikes off the back end and check the weight of the coach again. You only see an overall drop equal to the weight of the bikes and carrier but you'll also see a large drop of weight off the rear axle and a gain of weight on the front axle. The further back you get from the rear axle the greater the effect on the load on the rear axle. The chassis will act like a lever with the fulcrum at the axle.
Blue Ox has an easy formula to help potential buyers of motorcycle lifts to help determine how much weight the lift and bike will add to the rear axle. Using my gas coach with a 1/3 of the coach behind the rear axle adding 120 lbs of bike and carrier to the hitch receiver increase rear axle loading my 225 lbs.
Might not solve all your weight problems but will give a good head start. I will empty the coach each spring of everything and any item I could recall using the prior year doesn't go back into the coach.
Blue Ox Rear Axle Loading Information