Because we live in the heartland of federal/BLM land, if it's not posted private, no trespassing, we'll spend a night almost anywhere!! We've never been asked to move. We don't make a fire and never leave any trash behind.
Not sure what you mean by established sites? Established boondocking sites?
We try to avoid campgrounds most of the time, but we stay mostly in Nevada, Utah and Arizona.
National preserve areas that I've been in allow boondocking all over and that was straight from the visitor center. In fact they provided me some excellent ideas of places to go!