Disclaimer: I don't know the specifics of your situation, so perhaps this is laughable advice. If so, feel free to disregard it.
I would suggest thinking very carefully about whether you really need 4x4 or not. The NV3500 or another full-sized van would be, in my opinion, a much more satisfactory vehicle for you than a full-sized SUV. Most SUVs are a lot more limited by their GVWR than vans, and so it would be hard to carry the people and stuff you need in the SUV at the same time as towing a decent sized travel trailer.
For winter use, I can't think of too many situations where a van plus good snow tires would be inadequate, at least too many that I would in any way care to be driving in. I've personally seen vans go up some pretty steep and slick hills.