The fresh water tank under the bed is the least if your concerns if you are running the furnace or a space heater to keep things comfortable; especially if your electronics bay is located in the same are like it is in my Magnitude and you will get some heat generated by the converter and other electronics.
The bigger concern is the plumbing, which is not well insulated and can even be somewhat exposed to the outside for an outdoor shower, etc. If temps are only hovering around 32, you could be ok if you run the water now and then. Otherwise you want to open up the cabinets anywhere you can see the plumbing to let heat from the coach get into those spaces. A small ceramic heater can help generate heat in areas the furnace does not keep warm enough.
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