The fact you are moored, your hull is insulated below the waterline. Drain your water system, provide heat in the locker where your water heater is (htr has an insulated jacket)... I use an Extreme bilge heater. I use (2) thermostatically controlled electric fan heaters in the cabin area, one at the helm deck and one at the v-berth cabinet countertop. All cabinets doors (not drawers) are open, and access panels to the bilge are removed. Fan heaters provide heat and air movement.
Mind you, I keep my R27-OB at home, in the driveway and uncovered. I'm not sure if Knotflying realizes you have an outboard, but I don't see a need for antifreeze application to your motor. I also think your holding tank will be protected in bilge below waterline and heaters above in cabin. I had a hot tub cover (4"rigid insul) that I place on the cockpit deck.
My system seems to work well.
Bob
The Doghouse 2