Try Bar Harbor Campground. It is on Mount Desert Island, about 4 miles from the center of town, Bar Harbor. This is a family run CG that consistently gets great reviews on rvparkreviews.com. Check it out, their phone is 207.288.5188. Last I was aware, they do not take reservations so its first come first serve. However, it is a large CG with 300 sites and they are very reasonably priced compared to corporate parks such as Mount Desert Isle (avoid) or the generally well reviewed KOA's. I've been to Bar Harbor twice and on my third visit this would be my first choice. Also highly rated is Forest Ridge Campground and RV Park just off Mount Desert in Ellsworth which is the largest town around Acadia National Park. Very nice too. Good Luck.
2011 Georgetown 330TS
RAV4 on MasterTow Dolly