1. Shady Knoll in Brewster. Mid cape, not far bay beaches and trail trail
2. Atlantic Oaks in Eastham. quick access to rail trail, close to Salt Pond Visitor Center and cape ocean beachs and bike shops. Orleans not to far has shopping center. P'town campgrounds are nice but more expensive.
I have seen the rail trail patrolled so stealth camping is probably out and watch out for ticks.
only 1 campground on Martha's Vineyard and none on nantucket. Get the MAss. campground guide
There is a site in Trurp and 1( i think ) in wellfleet