You'll need to budget for groundrent. My parents had a static and the groundrent on a site with no facilities at all was nearly £2000. They bought a fairly old static and they were told after a few years that they either had to replace it or leave the site. They chose to leave as they didn't really want to fork out £0000s for a newer one, having picked up the old one for an excellent price.
They rarely, if ever, rented it out, although had a few regular families, maybe one or two a year, who couldn't afford anything else so my parents let them have it for a peppercorn rent. The site my parents had was very popular with surfers so tended to attract large groups of younger people, so my parents were very wary of renting to strangers. It gets quite rowdy in summer, it is very popular.
Out of season it was a fab place to spend a day or the weekend, and as it was so close to home (half an hour or so) renting it out defeated the object of having it. We had a great sea view, and we all found we returned completely relaxed. Many families there were second generation, having spent their childhoods there and had subsequently bought their own vans as adults. Lots of people moved in for the summer holidays, so again, less potential to rent.
A few people I know have overcome this problem by having two vans, one for themselves and another, plusher van for rent. They aim to keep one fully booked to subsidise the other.
There were quite a few handymen operating on site, maintaining the vans and the gas supply, so I would assume that someone similar would sort out a regular changeover contract if you wanted it.
Depends on the site, I guess, how booked up you'd be. The site we were on was so popular there wouldn't be a problem filling it, even with the lack of facilities. The waiting list to buy a van is so long it is closed.