I have bought and tried to rent out small RVs on small lots I’ve had, exactly as you are proposing. Here’s the results of that experiment:
You can buy small RVs for as low as $1,000 through ads in the local paper (about 24’ long). Finding cheap ones is not a problem.
From a landlord’s perspective, operationally, the biggest problem is the bathroom. We got repair calls constantly on the toilet, which is not really built for constant, daily use. In addition, you have the regular problems of people abusing everything so it falls apart more.
The biggest problem was the quality of the tenants. Who wants to live in a tiny RV in a mobile home park? The answer, some very undesirable people like carnival workers, drifters, and nuts. After a succession of horrible tenants, we gave up and sold the RVs back off and removed them from the park. I had hoped for clean-living contractors, but instead I got America’s Most Wanted.
Since the cost is so low, though, I would probably give it a try in your park and see what happens. We didn’t lose any money between what we bought and sold the RVs for, and if it works, it is well worth the test. I think that every park draws a different clientele, and this particular park was in a bad part of town and probably pulled a less desirable tenant mix than yours would.
If nothing else you’ll get some great stories out of it (see my story “Robert the Carnival Worker” in my stupid tenant stories).