We stopped at The Old Camp Casino in Burns, Oregon, last week. The sign at the campground entrance said to go to the security desk in the casino to register. We went inside and the security guard told us that it was $17.50 for hookups but that if we didn't need electric and water, we could park in the back row of the parking lot for free.
We parked in the back row (large-size gravel but level), alongside a nice grassy area, and put out the slide. It's away from the highway so there is no highway noise. And the casino closed at midnight so it was a very quiet night. We even heard coyotes yipping nearby and saw two deer on the grassy area right outside our window. Good place to stop if you're traveling on Highway 20 in the middle of Oregon where there's not much.