we have your 'twin', a Palazzo, and have traveled extensively... including freezing temps, snow, and sleet at the Grand Canyon's Trailer Village, Red Rock Park at Gallup New Mexico, a foot of snow and ice thru Tonopah Nevada(we then turned South and went to Las Vegas!), and the worst was probably several nights at the Thor Service Center in Wakarusa Indiana in February!.... but....
the only issue has ever been a frozen OUTSIDE WATER HOSE.
- your wetbay, if you keep the doors and entrance holes closed, should be fine, even when temps fall below freezing for a few hours thru the night or morning hours - it's not enough time to really do any freezing in water lines.
- your Furnace should also provide some heating to the wetbay
- and you can take more action, like we do, which is to sit a small electric heater in the wetbay, which comes on whenever the temps get too low, just enough heat to maintain above freezing temps in the bay, even if/when you're not using the furnace
- unhook your outside water hose, drain the water from it, and store it for the night in the wet bay, or even indoors - it's a lot easier to handle when it's not frozen!
- as for the gray/black tanks and the water tank - generally the amount of water in the water tank keeps it from freezing, even if temps fall below freezing for many hours - the gray/black tanks generally don't have issues with freezing for similar reasons, though you can make yourself feel better if you need to by running some hot water down the sink, and pouring some in the toilet at bedtime.
enjoy.... : )
'14 Thor Palazzo 33.3 compact diesel 100k+miles since '14... US, Alaska, Canada...
AND a '14 Gulfstream Amerlite
AND a '07 ForestRIver Rockwood