We wintered in our fulltime for 3 years in our home location. Freezing is one thing, sub-zero is another.
also keep in mind all motorhomes are different and will therefore deal with the cold differently.
The best thing you can do is monitor your wet bay temps with a weather station temp sensor, one that will have the read out on a panel indoors.
If you plan to let it sit I'd just winterize it and be safe. Trying to keep it thawed will just use up a lot of propane.
If you'll be living in the rig, then be prepared:
*if the wet bay temps drop to near freezing even with your heat being pumped to your wet bay area put a 60W bulb down there near the pump. Some folks put a small electric heater in there or halogen lites but I think those are too hot and a fire hazzard.
*have plenty of propane onboard...in the coldest weather a full tank may only last a week. Have a back up plan if that tank runs out.
*use a small electric heat to warm up cold spots but don't depend on it to warm the coach. You need the furnaces to run so warm air is pumped into to your water bay.
*if you kitchen sink is on a slide...keep the lower undersink doors open when the outside temps are near or below freezing. If needs be pull in the slide. Our sink lines would freeze when the temps dropped below 20 even with the doors open. We had to pull in the main slide when it got cold.
* if you still freeze up...winterize the rig and shower, cook and use the bathroom elsewhere! We lived in ours winterized one year but it wasn't fun!
* be mindful that an absorption 2 way refrigerator does not like cold either. In extreme weather it can stop working until the outside has time to thaw. A drop light can be added to that outside area as well and some of the outside refrigerator vents can be covered but don't seal it up. Usually it takes extreme &/or extended cold to shut down the refrigerator.
*Common sense things...keep shades and curtains closed except when the sun is not shining in, add extra throw rugs to make the floor feel less cold. Even with heat being pumped into the lower bays the floor will still feel cold.
*Use an indoor humidistat to monitor those moisture levels. If you'll be showering indoors...vent moisture outside daily. When the outside walls are really cold they can collect condensation that can freeze, dampening the contents of all cabinets and cause mold. Therefore pull all clothing away from the walls, pack loosely/sparcely and leave at least one door open to each compartment to equalize the heat. This happened in our very arid climate where we had to run a humidifier 24/7 because the furnace ran 24/7 which dried out the air to a not human friendly-20%. Any humidity at all will cause condensation on the walls and windows. Dry off these areas daily.
*drafts...if you get cold winter winds...you'll find out if there are air leaks around your slideouts!
Winter is doable but after 3 years in our rig in it down to -25 at times...we'd rather be in our house!
2002 Tiffin Phaeton
2005 Malibu Maxx toad