Greetings!
Unless you’re actually planning on using a gym to exercise, I think they’re a huge waste of money. No camping setup is complete without your own toilet and shower. With a van, even a minivan, you have plenty of room. For a car, you can get a pop-up shower tent, or shower in a swimsuit. You can also shower while seated in a low top van or even a minivan.
The bottom line is that you can have your own for less than a month or two of a gym membership, and the convenience factor is huge.
I’m a pretty firm believer of being as self sufficient as possible, and I feel this gym membership thing is just one more money making scam conjured up by the promoters. I prefer my own shower, but if I want a fancy one, I can get a free shower at almost any truck stop. The truck stops give the truckers free shower tickets, that they rarely use. You can often find them on a bulletin board, or in the laundry room. If not, most truckers will gladly give you theirs if they’re not going to use it themselves.
Sink baths also possible and not much of an inconvenience. Typical campers have no problems staying clean without the cost of gym membership.
Cheers!