Getting ready for cold weather entails making sure your black water tank, gray water and fresh water inlet are protected from freezing.
Our RV has a compartment that is quite small however we did find a way to keep the temperature above freezing without placing so much heat in the area that would cause the holding tanks to melt. We used a small shop light with a 40 watt bulb. If the temperature drops below the heating effect of the 40 watt bulb we can replace it with a 60 watt or even larger watt bulb.
We also placed a thermometer in the bay so we can keep track of how well our heating bulb is doing. Next we wrapped our water line with low a wattage heat tape, placed insulation around the line and tapped over the insulation.