I keep my F17 outside during the sailing season in MI, but then put it in the unheated garage for the winter. I have mast cover to keep it out of the sun and I have a plug I remove in the mast base to vent it for the winter. I have a 9 year old carbon mast and the freeze thaw cycles haven't created any problems yet. I try to make sure the boat is tipped so that water can't collect in the bows and freeze, that would definitely create issues.