We stayed in Lamoine State Park and Camden Hills State Park. Both had electric. CH sites also had water. Both were on/near the coast, close to town. Both allowed dogs. Neither had a trailer park feel. Lamoine will be a little more difficult for a large trailer if you manage to get a waterfront site. CH is mostly in the woods. Both state parks are in great touring areas.
We also liked Seawall (excellent location) but it has no electric.
On the way to/from Maine, we stayed at Harold Parker State Forest. It doesn't have electric or water hook ups, but it is in a prime location to visit Glouster, Salem, Lowell, Concord and Lexington. The sites are large and spread out though there are a couple of turns in the campground that are a little tight.