I wouldn't worry too much about freezing once you get to South Carolina. Hell, we didn't worry about it living in Stamford CT over the winter. If the water doesn't freeze, neither will your boat.

That being said, I'd be more concerned about protection from storms. Osprey Marina in Myrtle Beach, SC is an excellent place to keep your boat. It's off the ICW, up a narrow channel to a small pond-like marina protected from all sides.

Brunswick Landing Marina in Brunswick Ga, where my boat presently is, is just north of the border of Florida, is also an excellent place. There are 314 slips here and it's a hurricane hole. There's no current and a large liveaboard population to watch over your boat.

Certainly, with five weeks to head south, you can get as far as you want to. Do either Osprey or Brunswick.