Then there is the area directly south of Castine, to the east of Holbrooke Island -- but you can't get too close by car to that location, if you were going to commute there.

I got decent Verizon service neard Holbrooke Island -- and it's more sheltered.

Smith Cove offers some possiblities.

On a general note, I think a commute would make Rockland, Rockport, Camden, and (maybe) Belfast would make pretty nice possiblities. Stonington is another (but less sheltered).

Personally, Rockport and Camden are really neat places -- but more expensive to keep a mooring.

If you're seriously "commuting" back and forth, Portland is (potentially) less expensive to fly in- and out-of. But driving from there beyond Casco Bay would be a factor that would change convenience of a long-weekend sojourne.

I know some people that decided that they'd rather fly-up and spend their (limited time) up in New England's better cruising grounds, rather than spend the time taking the boat up and back.

I happen to like the passages as much as the gunk holing -- but different strokes for different folks. Moving a boat earlier or later in the season can be a very different experience (especially later).