Lake Murray is just outside of Columbia, SC by about 30 minutes to the NW. We are at Winward Point Yacht Club/Marina. There are a couple other ones as well...Lake Murray Marina and Columbia Sail Club. Columbia doesn't have live aboards though. It is a good size lake with a couple of island in it. I cant recall How big it is. Here are the links for the two marinas that will let you live aboard. Winward point will be cheapest but really no frills.
Here is some info on Lake Murray as well.