I found one it Tucson, in the University area--not really close to me. I'll check it out if I'm in the area--a driveway behind the house for $15 (per night probably)
Looks like it is JUST parking, not for staying in overnight, but if self contained, and you are very quiet, may work for a night or two. Since it's behind the house, overnighting may be okay. Still need to find out.
What is that other one, for boondocking on private property? Can't find it now.