Older thread, but I'm at The Harborage at Ashely Marina. All the slips here are privately owned. Check craigslist or other local classifieds for available slips. You can also check Bohicket Marina on Seabrook Island or St Johns Yacht Harbor on John's Island. Another good marina is Charleston Harbor Marina in Mt Pleasant. They "technically" only have 6 liveaboard
berths, but I know at least twice that many that live there. There are a TON of good marina's in Charleston, it all depends on how far you want to be from the harbor. I can be at the jetties in about 45min from my slip, whereas from St John's it's going to take you 3-4 hours depending on tides.