I was up that way a few yrs. ago. Took the trip with just my dog and myself. If you want to see what's left of the old Maine sea coast head as far north as you can. You'll get away from all the tourest traps so to speak.
  Once up that way look for seafood wholesalers, you may see signs posted along the highway, that's how I found the one I did business with. Some of these guys will sell to the public but kind of dislike tourests too, wonder why !!! I bought maybe a 7 lobsters alive that I brought home with me along with fresh scallops. Don't be afraid to hit the docks when the boats come in too, they will sell them right off the boat if you talk to them. 
  To bring them home alive this is what you want to do , in a large cooler with maybe 3 inches of ocean salt water , no other type will keep them alive, place the critters in it. Then with newspaper soaked in  ocean salt water , cover the critters.  This trick was taught to me by the guy I bought them off of. You should be good for 24 hrs. this way, I lost one and had to cook it on the way home, broke my dogs heart and myself to have to eat it , not !!!
  I used a woodall's camp directory and it was on the money on the places I stayed.
  have fun and a safe trip for sure !

We went to a rally at Chewonki campground in Wiscasset a couple of years ago.
It's a little bit further north. It is not a cheap CG, but well worth every penny.
We stayed on site 13, if you click on the map I've linked here, it will show you the view.

http://chewonkicampground.com/map.shtml

Site 13 seemed to be about a 1/2 acre with one of the best views in the park. It had water/electric.
The pool is salt water. Not sure if it's open in Sept though. If I recall correctly, there are about 50 sites on 50 acres....
I would very highly recommend Chewonki.....
Lots and lots of seafood restaurants in this area.

If you want to head a little further north of Brunswick, we stayed at the Bar Harbor KOA a few years back.  I seem to recall it being a nice place, although there sites were a little on the small side and there wasn't a lot of shade in the area we were in.  We were in my FIL's class-B, so we didn't need a ton of space, and it was later in the year, so it was cool so we didn't really need the shade either.  It's close to Acadia National Park, which has lots of hiking/biking opportunities.  You can also head into Bar Harbor itself if you want to do some shopping or hit some restaurants.  I'm sure there are other things to do, but we only had a couple of days to explore when we were there.   

http://goo.gl/maps/jQfy9