What's important is that Craig is seeking information about a place to leave his boat and dinghy that he can get to reasonably easy by car. Rockland fits the bill quite nicely, as it's not only accessible by car, but there's a bus line that takes you there too. He might even be able to arrange a one-way rental with Enterprise (though it's a bit of a poke from their South Thomaston location to Rockland). Even better, Rockland is a two-hour sail to Vinalhaven and North Haven, which offer any of a number of places to visit. From there, go through the Fox Islands Thoroughfare and across East Penobscot Bay and you're in Merchant Row. That's pretty sweet.
Belfast is a nice place too, but it's kind of off the beaten path, is not as favored logistically, and isn't quite as close to some of Penobscot Bay's most special places.