In Crested Butte, check out the Washington Gulch area -- lots of sites, not far from town. The weekends get kind of busy, though.
Near Ridgeway, check out the south end of Silver Jack Reservoir -- again, lots of sites, not as busy. You can get there from Cimarron, as well as from Ridgway.
You probably already know this, but here is a tip -- download the Motor Vehicle Use Maps from the national forests. They show the roads that are open to boondockers.