I guess I am not familiar with any cemeteries which are not on private land of some sort. Just because there is no gate, lights, or groundskeeper does not mean it is public property. Even though the residents are quiet, it seems like it would still be trespassing to me. And the presence of an RV would certainly capture the scrutiny of any law enforcement driving by.
I could see a maybe, for rural cemeteries that are partially abandoned and out in the boonies. But if I am out in the boonies already, there are plenty of spaces to go camping without seeking a cemetery. So even then I don't see the point.
-Eric