Mine was just drained and opened up last year and stored in a pole barn by the previous owner and then myself before the season. My barn is insulated and on real cold spells (-10F at night) the barn sits in the teens without the heater. Boat was fine and no issues. In NC, I wouldn't worry about antifreeze at all. Maybe get a nice tarp to go over the cover and keep the heavy rain out, just make sure some air can flow under the tarp so you don't get mold growth.