Open parking lot available for camping at the American Legion in Borrego Springs for military veterans. Some spots have full hook ups. Minimal cost to stay there. Think it's 5 or 10 bucks. They have a flush toilet, shower and, of course, a bar. Cash only for the booze and dinners.
I like staying here during the Tierra del Sol event. Close enough to access TDS and far enough away from the craziness.