We just came off the Magic a few days ago and we parked in the Port of Galveston garage. It is so close there is no shuttle. We walked out of security and were on the road in about 10 minutes. I would definitely prearrange it to make sure you can get a spot because it was pretty full when we got there at noon. They also have an express lot right next to the terminal that is even closer. However, that one seems to fill up pretty quick and has to be prearranged as well. They offer Parking Lot B for less money but it is across a busy street and most people take a shuttle there. All lots are less expensive if you make reservations and pay online.
I know there are other lots available but we were more than happy with our experience in the garage and how easy it was to get to/from the port. We parked and just rolled our bags to the terminal but if you have a lot of bags (or small kids) you can always drop them off and then park. It's still super quick.
sign is as a member and try. Strange it isn't giving you Lot B option. When I signed in as a member, it added the garage. Maybe try signing up as a member and then see what happens?
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