We have a 2009 Itasca Navion 24A and have realized it has fairly minimal equipment designed for winter use. One of the biggies for winter use is to keep your fresh water from freezing.

The solution I came up with was to buy two small 12v space heaters. One for the underneath compartment where the water valves and pump are, and one for the area under the sink that has the rest of the water related equipment.
In order to save electricity, I installed a thermostat switch that turns on at 35 degrees F and off at 45 degrees F. You can control how much heat output you want by how close you put the thermostat to the heater.
If the space heater is not for you, an alternative option is to use an incandescent bulb. A 12v one would likely be more efficient as then you wouldn’t need to have your alternator on if you’re not using shore power.

Bonehead Move #1
We tried soldering the wires to the leads on the switches. As it turns out, our soldering skills are not super good and this is far more difficult than it needs to be. A better solution is to just get some wire connectors and slide them on to the leads. If the connectors are a little big, you can crimp them slightly and that should do the trick.