I would hazard to stick my neck out and say that crossing Casco Bay cannot be a level 2 trip by definition -- "a landing place within one mile" (or some such wording)? It can only be described as level 3, if you go into the trip level definitions.
Secondly, what is a level 2 minus? I have heard talk of re-defining trip levels, but there is no such thing mentioned in the above same place -- only "level 2" and "level 3".
"Inner" Casco Bay can be quite daunting at times, what with plenty of boat traffic in summer, ships coming and going, channel markers everywhere and lots of fetch from the south. Treat it with care.
By the way, you call Fort Gorges "ancient"? It's positively brand-new, compared with, say, Rheims cathedral!