Don't forget that when water freezes, it EXPANDS.
So its important to get ALL the water off the boat. ice forming in your drains and other crevices can create force enough to crack things you dont want cracked.
you have a nice boat. worth spending 40 or so bucks on a tarp for. If you do cover it, be careful that you don't leave any place for snow/ice to collect, or the weight can pull the stanchions in.
the best solution of course to all of this is to spend some quality time in the tropics.