[Daryles]

As mentioned above, put a small heater underneath along with a remote sensor.
I have 3. One outside, one in the underbelly, and one in the battery compartment.
Another way to put heat into the underbelly is to remove the left side panel undervyour kitchen island sink. Behind there you will find a hole where your sink drain goes through. This leads all the way down to the top of your galley tank (underbelly). I hung one of the remote thermometers on a string and lowered it down there. You can put a small heater, hair dryer or computer fan blower to push warm air down there.
Don't forget to turn on your tank heaters when you know it's going to be below freezing.