In the Charleston Harbor area Charleston City Boat Yard up the Wando would be my recommendation for dry storage
it's well protected and great people, you'll have to call for a price
. In the water
you're looking at 10-14 a foot depending what you're looking for. Charleston City Marina and the Ashely Marina are on the Ashely River then Patriots Point, Maritime Center and the Copper River Marina on the Copper River. There are others but those are the bigger ones. Mt Pleasant has Hobcaw as well but I don't know if they can take a 47' sailboat.