Cold water boating - what to do??

I live in Wisconsin and have a 1992 SNOB, and unfortunately, the temperatures will begin to drop below 32 degrees in a matter of weeks. I would like to continue to ski through October, but don't want to risk cracking the engine block or anything else. I keep the boat on a lift. When do I need to do something additional to the boat to extend my season, and what do I need to do to the boat exactly when I'm done running it for the weekend and put it back on the lift for a week? I'd like to hold off on winterizing the boat as long as possible. Thanks.

I have, on occasion, put a light bulb (burning of course) under the engine box whenever the temperature was expected to dip below freezing and I had not winterized the boat at the time. The light bulb should keep the engine area warm enough to prevent freezing. Just make sure the bulb does not touch anything that will catch fire or be damage by the localized heat.