We taped silver-sided bubble wrap insulation (from Home Depot) to the cabin top and inside of lockers. Virtually eliminated the drippy condensation issues. Instead of shrink wrap, we used translucent 6-mil drop cloth weighted down with partially-filled antifreeze jugs scrounged from the marina - as someone else here said, you WANT some kind of venting.
An oil-filled electric heater - looks like an old-fashioned radiator - made the boat cozy with zero carbon monoxide worries. But that depends on how your marina charges you for power usage. If you use an espar, etc - make sure to install a CO detector.
Get 2 pairs of 'Yak-Trax' or similar snow cleats from REI, EMS, or other outdoors store. Keep one pair in your car (if it snows while you're away from your boat) and another in your cockpit (if it snows while you're home).
Make a deal with your neighbors re: water-tank-refilling parties. Many marinas turn off water taps at the docks during the winter, so you have to roam farther to get water. You and your neighbors will have to chain all your hoses together to reach the taps on land, pick a relatively warm day and fill everyone's tank at once.
There's a wonderful sense of cameraderie that you and the other hardy souls will share - enjoy it.