Salvo,
I think that Navion of yours has a fairly long wheelbase relative to it's length - which definitely helps with loads cantilevered off the rear not unloading the front end too much.
Sometimes I wish our Spirit had a longer wheelbase relative to it's length (24 feet long on only a 158 inch wheelbase) so we could carry an offroad motorcycle on the rear. In my case, I'd better carry a motorcycle on the front instead. I do love the short turning radius of a 158 inch wheelbase, however.
For what it's worth, my ideal offroad two-wheel vehicle to carry along on our RV trips would be a Honda Big Ruckus. Here's what they look like: