David:

You're going to Yellowstone this time of the year? I've been there in July and it snowed. Traveling from Georgia to Wyoming is not a good idea this time of year, especially driving a vehicle you don't have a lot of experience with. You will undoubtably encounter icy roads (black-ice) along the way. Personally, I wouldn't do it!

Campgrounds? I don't know of any in that area that are open in the winter do to freezing water and lack of customers.