Mammoth is the only campground open. Only BAT (list available from NPS) machines are allowed on the park. Also, almost all trips must be guided. There is a lottery system for unguided permits. Almost all snowmobiling in the park comes out of West Yellowstone which will be 150 plus miles from Mammoth one way. Strongly advise leaving the RV behind and use a hotel instead. Yellowstone and vacinity is decidedly RV unfriendly in the winter.