The GAP is only from PGH to Cumberland. The C&O is from Cumberland to D.C. No need to stealth camp on either one as there are sufficient, established camping options. There are also some B&Bs and guest houses along the GAP. Look at the official site for a list. I stayed at the camping area with Adirondack Shelters in Connellsville (free with grocery store 300' away) and at Husky Haven Campground in Rockwood ($10). Nice place with right along the trail with free fire wood and tons of shade, but bring ear plugs:
There is a companion guest house across the river in town. Camping fee includes use of showers and Internet at the guest house. The grocery selection at the Dollar Store in town is weak, but there are a couple of places to get prepared food. I would avoid the commercial campground above Connellsville. It looked like combat camping at its finest. When I rode by there was loud music playing at the pool area.
Stopped to patronize this place. They had old skool Mountain Dew made with real sugar.
Haven't done the C&O, but many people say it can be extremely sloppy after extended periods of rain. Did the GAP on 32c Conti IIs. No problem.