If you decide to over-winter in the 5th, skirting would be a must have. You could place a couple of heat lamps or small electric heaters underneath to maintain a decent floor temperature. Any pipe, drain, or tank outside of the heated and skirted underbelly needs to be heated with cables or pads to function. I know one member on here that popped the cap off his drain and used handwarmers in the pipe to facilitate dumping.
I would suggest a different course of action, though, considering your overall plan. Instead of paying for campground fees, I'd put the money into paying off that land you're looking for. Of course, I don't know your exact financial situation but it may be a better overall situation to buy the land, improve it, and then park your 5th. You could start small with just the basic utilities. If it was me, I'd definitely look into building a large garage. The garage would be heated and serve as living quarters, also. Maybe that's just the Contractor in me wanting to build something but I think it has some merit.
Good luck with whatever you do, I enjoy reading about folks who think outside of the conventional box.