Acadia NP might be close enough. For that matter, Acadia NP should be close enough even if it's farther than you really want to go.
Quite a few amusement parks have campgrounds associated with them, actually. Offhand, I know of Knoebels and HersheyPark in PA, and I think Darien Lake in NY may still have one. Of those, Hershey would seem to me to be the best choice for a week's vacation, since there's a good bit to do in the area besides ride the rides and enrich the midway's coffers. (Knoebels and Darien Lake are basically out in the middle of nowhere.)
