Fantastic info! Thank you. I've never dared to nose my way into the inner sanctum, and I'm guessing that neither did Hank Taft! The problem of course is that the high tide required to get in leaves no margin for error if you should go aground.
It sounds like you might want to try Seal Trap on Isle au Haut's west side. It's not in the guide, and it is not for the faint of heart.