[TrueBlue]

The greatest problem, as I know it, with keeping any boat uncovered during sub-freezing temps relates to water intrusion. The slightest gap between materials, or minute fiberglass cracks, will wick up moisture through capillary action. As this water freezes and expands, the gaps & cracks increase in size. Several freeze & thaw cycles could result in some serious damage, not to mention the risk of water entering finished spaces below.

I personally, would never leave my boat uncovered through winter storage, although many boat owners at my marina do. The teak decks of my boat are especially vulnerable. Even though there is solid fiberglass beneath, freezing water is a sure way of popping bungs or screws and delaminating planks.