I'm in the frozen tundra of Vermont. It's my first Winter with my 1997 Wave in my door yard. I unfortunately was not able to arrange indoor housing for my boat and normally condensation provides several cups to quarts of water in the hulls per month. I'm concerned about the residual water in the hulls causing cracks. What about putting something like car windshield washer fluid in the hulls to keep the water ...um ..water? Has anyone tried that? Any harm done?
I wouldn't use windshield washer fluid because the "antifreeze" in it is alcohol - a solvent.
If you're really worried, put some regular (full strength) car antifreeze in. I do it every winter on my 17 wing tubes that are a lot more susceptible to freezing/leaking.