Ditto Acadia in Maine! We've stayed at both Smuggler's Den and Mt. Desert Narrows up there and like them both. Smuggler's Den you can hike the west side of Acadia trails right from the CG, which is nice. Mt. Desert Narrows was pretty convenient for getting everywhere by car or shuttle. So much great hiking and biking up there! Although, it really is getting a bit too popular for it's own good and can get super packed in the summer. It doesn't take much, though, to get away from the crowds out on the hiking trails.
On the way up there, you could think about stopping in Freeport at L.L. Bean and maybe take in one of their classes. DH and I did that a couple of years ago and had a great time doing their shotgun session. Cedar Haven CG is nice for a Freeport visit, smaller and well-kept and outside of Freeport so pretty quiet, but convenient to town. And then from there, a stop in Boothbay would be nice too. If you are into craft beer, you could consider staying at Boothbay Craft Brewing Co. They have a handful of full hook-up sites and some cottages as well.
Whatever you do, make sure to make reservations sooner than later. The summer season really books up!