Hi,
You need to protect the fridge. See the winter camping thread on the full time forum.
I would operate off the fresh water tank and not use the heated hose.
I would not dump the fresh water tank.
I would not shut off the fridge as restarting it in the cold may be a pain you wish to avoid.
Make sure the drain tube for the fridge does not have a "loop" in it in the way you would want for summer operation.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.