Patrick,
You may or may not have bay heaters. My 99 CC does not have electric bay heaters. The manual says use the hydronic heat or drain the pipes to ensure the bays don't freeze.
It has been really cold here for the last week, and I turned on my Webasto a couple times to make sure it working, but all I am really using is a space heater inside the bus set to the low setting (800 watts) and a 100Watt light bulb in the plumbing bay. This is the procedure I have always used, and it worked great in Yellowstone for two seasons and has always worked here. When it is 20 outside, the bus is usually 55-60 degrees inside, and the bay is well above freezing.
Of course, the manual says if you are going to leave the bus unattended in cold weather, you should drain the water from the systems. I fill my fresh water tank almost full, and use the procedure above. Maybe you have the bay heaters, but I would verify it before I depended on them. I had them in my Marathon, but I never trusted leaving the bus unattended with water in the system and depending on the bay heaters. I always assumed the power could go off or a breaker could trip, and I would have frozen pipes.
Because my bus barn was an add-on of an existing building, it is not insulated, but I just bought insulation last week, so I can do it before summer. I am much more concerned about the heat than the cold, but I understand cold is a real problem for most people. As Jon has mentioned, I also have the service pit that helps moderate the temperature.
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