We have an '05 Sienna. Towing cap. 3500 lbs. We want to tow a 2742 lb Trailmanor (dry weight) with a 351 tongue weight. That leaves a mere 407 cargo weight.Is this doable? Are you suppose to max out on the towing cap. or is there an 80% rule? If we get a weight distribution hitch does that add even more weight?We just want to go camping without tearing up our new van.Help!!!!!