I'm also sailing in October out of Boston. I'm using the parking associated with the cruise port. If you go on parking.com you can find your sailing and make a reservation. They have a special cruise rate The parking is on 93 Fargo St. I plan on dropping my family and luggage off at the terminal then parking the car. They offer a free shuttle from the lot to the terminal. Otherwise, It's a 10 minute walk. I used to park at the C1 parking lot that is located adjacent to the terminal but that doesn't look like it's cruise parking anymore.