If storing outside I would pour RV/Marine Antifreeze (Pink Stuff) http://www.peakantifreeze.com/rvmarine.htm In the Livewells and recirculate through the pumps, also pour some in the bilge area, pour down pump-outs and bilge tubes outlet ports, this will make sure if any moisture does get inside boat it won't freeze and bust a bilge or recirc pump.

Fill up the fuel tanks and trest with Fuel Stabilizer. A full fuel tank will not cause condensation like a partially filled tank. This will help keep any moisture out of the tanks. I also fill the oil tank to to prevent condensation. Heating and Cooling during the change in temperature will cause condensation.

If you are concerned about mice. What I do is take some rat/mouse poison in pellet form and wrap in aluminum foil. Use 4 to 6 pellets per ball and make same balls or nut sized balls. They carry these back to their nest and consume them. Make sure you do not have kids or pets that will get into area or boat that may consume the small balls. I use these in my boat garage and is the most effective and do not have mice problems anymore. I read this on Pest Management Forum and has been extremely successful for me.

I hate winter! Just bundle up and go fishing! You just need to get a bigger ice auger like a 20' Footer!