There are blm free places on the east side of the dunes along Ogilby rd north of the railroad tracks. You will be sitting on the west side of the Cargo Muchacho mountains. You can go back in a ways towards the mountains so that you can access the trails back there without dusting everyone out who is parked more towards the road.
Ogilby rd exit north of 8, along Ogilby rd it's pay for ltva blm camping with tons of room.
If you go a few miles farther west oon 8 you will come to grays well road with blm camping and dune riding. Dune permit is required. I wouldn't worry about it as there appears to be open riding area that dont put you in the deepest part of the dunes. The Glamis area may be a little more action packed.
I also stayed up at big river blm land just outside Parker. You can go back in a ways and ride the trails toward the mountains. Same issue with the dust. Watch closely as your gps zeros in. Don't go past the nub of a hill as you go back in. You will see that it gets much too rough.
On the other side of Parker is an area called swansea. I have driven through there but not stayed. you have to go out a ways to get to the area where camping and riding is allowed. There is an info board that is a couple hundred feet from the highway. Poor cell signal out there.
We stayed along Plamosa road between Bouse and Giss pass and there seem to be a lot of trails around there but check the blm trail maps for these areas before going. There is a fourwheels club in bouse that has some info on their website.
These places are on freecampsites.net