There is a difference between Boondocking (legally dispersed camping in your RV) and Stealth camping (illegally camping).
The OP is asking about how to find LEGAL places to camp not about illegally parking.
There is also a difference between folks who are looking for a free place to sleep and those looking for a boondocking site. The former will select rest stops, walmarts, etc. The latter is going out into nowhere to spend time (rock hounds and geo cachers are this type).
It sounds like the OP is looking for the latter - places of scenic/wild beauty to enjoy a few days.
OP - make friends with your national forest stations. Go online and check for any BLM or national forest/grassland areas that interest you. The website will usually say whether dispersed camping is allowed. Dispersed camping is similar to boondocking - dispersed includes hiking in, so may talk about trails, etc., as well as roads, so pay attention. Now that you know if it's allowed, you have to start hunting down actual sites.
One way is to stay at a campground for two nights. The first day, go drive the roads and look for potential sites. Be sure to pay attention to the type of ground - don't want to get stuck. The second day, move out to your selected boondock site.
As you do this, you will be able to skip the campground and go straight to a boondock site. Then you can spend a day looking for new ones further out.
If you do it locally for a while, you'll get more and more comfortable with the process and will be able to "take it on the road".
A fellow camper gave me a few boondock locations to check out. I made a day trip to check them out. Other than the fact that they were free, I found them lacking in beauty. Two were simply dirt parking lots on the side of the road. The other was set in the pines and was fairly pretty, but the nearest water was several miles away - there was a very popular hiking trail close by but it was very active. In comparison to them, my favorite campground is well worth the $20 a night - it has a creek right there, only eight sites on my loop, and hiking trails that are less populated. I have not given up on boondocking, but I realize that some are about camping cheap and some are about getting away - knowing what you want is important.
