Is it a full wet bath with sink and shower, a toilet with holding tank only, or a porta-potty closet? Is it functional, or could it be made functional without too much work? A bathroom, even a small one, might be nice to have for midnight runs, Walmart overnights, and the occasional campground with dirty or crowded bathrooms.
It might be worth trying it out for one season. If you do decide to turn it into storage, leaving the walls and plumbing in place would make the decision reversible if you, or a future owner, find your needs have changed.