There is ample parking available at the Port of Baltimore. A shuttle bus will take you to the ship. The fee in 2003 was $7 per day. There are sea containers at the parking area for you to drop off your luggage just prior to parking your vehicle.
We also cruised out of Baltimore on the Galaxy in 2003. The parking is very well organized and the area is secure so the chances of vandalism or break-ins during the cruise appear to be minimal. If you go to the Port of Baltimore web site (use Google or any search engine) it will give you specific directions on how to find the parking area from the nearest interstate highways. Once off the interstate, the roads are also well marked.