Here's another thought for you... They just open the new Schoodic Woods Campground is located on the Schoodic Peninsula section of the park. It's in Winter Harbor which is across Frenchman Bay from Bar Harbor. Here's the best part, they offer free water shuttle service to Bar Harbor which you can pick up several different tours of the Park (even hiking tours).
I really wanted to stay there this time, but I was afraid my RV would be to big and I really like Oceanside KOA.
Here's a link to it:
https://www.nps.gov/acad/learn/news/acadia-announces-the-grand-opening-of-schoodic-woods-campground.htm