Where are you?
I'm lazy, so I didn't do any research to see where you are, but I have been sailing in the winter on the Potomac River for the last three years. I only day sail, so nothing is used but the engine, and that is winterized as you described by running non tox antifreeze through it. You should install a y valve near the raw water sea ****, and when you are finished sailing you simply flip the valve, put the free end of hose in the bucket of anti freeze, and run the engine for a few seconds. Very simple, and extends the season.