Cobscook State Park in Maine on a tidal cove is lovely. The reservations fill quickly, but there are some sites that cannot be reserved so you might be able to stay on short notice. We also enjoyed Grand Isle on Lake Champlain in Vermont. Camden Hills State park, midcoast Maine, is pretty and only a few miles from Camden Harbor. A small fleet of wooden schooners offering sunset, day, half-day sails moors there. Acadia Park's Seawall and Blackwoods campgrounds are fine places to stay, and the park has wonderful hiking trails with long views and hidden ponds. There is a new campground, in the Schoodic section of the park to the east, that I have heard is geared toward the enormous campers some people have. The other two are more to my liking.