I can't comment any on the MABDR, but I can recommend two good dispersed campsites that appear to be near your route.
1. 37.79222, -79.12929, there are several sites near here, along FR63. It's very pretty, and right along the Piney River.
2. 36.66970, -81.48699, this is a large site called "the scales". It's a very pretty area with wild horses and pit toilets. Tight road to the site though, I would not want to bring a trailer on the switchbacks.