September up this way is the best.  Most of the tourists have gone, and it's too early for the bus tours with the leaf peepers.  I'm not anti-people, but the coastal regions can really get crowded.  In the Bar Harbor area, we preferthe KOA Woodside -- cheaper and more services.  Get a place way back in the field.  Cell phone service is spotty and television is non-existant without a dish.  Bring cool weather clothes -- layering is best.  We'll be there mid-September.  In the mid-coast, Saltwater Farm in Thomaston is our favorite -- very quiet, but close to everything.  We'll be there in July.