I've stayed at Somes Sound View Campground a couple of times. I think it is where Dave was attempting to recall. Danielle did a nice job of description - there is also a Quary, and like she mentioned, there are sites right at water level on sand. There are also some wooded sites a bit away from cars and RV's - this is not a rustic campground by any matter.
The place Rick suggested sounds excellent. Like this one, Somes Sound is also a 20+ minute drive into Bar Harbor... crowded, Bar Habor... you see lots of wildlife on the way into town and you're in better placement for some "out of the way" lobster pot restuarants around the backside of the island. Plan time in your schedule for Tea at Jordan Pond House.
I've never stayed "inside the park". Congrats on the wedding and enjoy the isle.