If you not going to be using it for the whole winter season then just winterized it. Easy enough, and then your not sucking a ton of electricity all winter long. Block heaters are to get an engine warmed up quick to make cold weather starts easier, not really to maintain a constant long long period temp. I agree otherwise with the dual light bulb set up, but if you can afford a $20k+ boat, you can afford to winterized it and KNOW your engine will be safe all winter long. Just my opinion, and did not mean any of it to be rude.