I've used antifreeze for years, you need to really flush-it. I've found that two or three full system flushes works for us. Our boat sits in the water and consequently it really doens't see quite the hard freezes that it would in a more northern clime plus sitting on the hard.

Certainly DON'T let your equipment, tanks, lines, or fittings freeze. Blowing out lines might work -- but then again that isn't assurance for all conditions where water might be "trapped".