My favorite place on the planet!
McPhee Reservoir has some kind of formal status as a national recreation area, so camping is allowed only at the few developed designated campgrounds.
House Creek Campground, info HERE.
McPhee Campground is on the other side of the lake.
There's nothing rustic about these campgrounds - they are developed and there will for sure be a fair number of RVs. Not cheap, check the web sites but it looks like "standard" campsites are $26/night. We drove to House Creek Campground one time just to check it out and there was hardly any shade.
A really nice private campground that does have some tent camping right by the Dolores River is Dolores River RV Resort. Lots of big trees, lovely. Looks like a tent site would be $32/night, but the campground does have WiFi, so there's that.
I just called the Tres Rios Public Lands Office (combined Bureau of Land Management + San Juan National Forest) just outside of Dolores, and confirmed that there is still dispersed camping all along Boggy Draw Road, which is by the extensive Boggy Draw Trail System, many many miles of mellow single track in the Ponderosa Pines, just a mile or two above Dolores.
The super mega everything map for all SW CO singletrack is put out by biglooptrails.com/colorado-trails They seem to be doing a good job of creating new editions to stay current on all the new trails being added to both Phil's World and Boggy Draw.
You can get a digital version as well, but I'd recommend the paper option for your personal sanity and the great overview.
If you're in north Austin (Walnut Creek area) I'll be glad to share my maps with you. Just PM me if you'd like to meet up. We're retired, so mostly open schedule.