6 million acres of free camping in the USA...why would you be sticking to rv parks?
I guess if you need the hookups...
Just in WA state there are some great locations. Anywhere in the Mad River area near Entiat is very pretty. Blewett Pass area has a lot of BLM land that is gold claimed, but most of it is public and you have the right to be on the claim as long as you are not mineral collecting. Actually joining a gold prospecting club with a lot of claims is a nice way to boondock without feeling like you are out of place. A plus if you actually like to pan :)