In reply to Michael Morrell:
The National Trust site near The Old Dungeon Ghyll Hotel is the nearest to Gimmer, you would walk in to the crag directly from the site and leave your car there. The one in Chapel Stile is long walk from Gimmer, 2.5 miles further away than the NT site. If you camp there and drive to get closer you'll end up parking almost next to the NT site anyway and then have to pay for parking on top of the campsite fee.