We've driven about 600 miles while well below freezing and no problems. Spent several nights and no problems with freezing. The furnaces provide some heat in the compartments and they are all tight. No light gets out when you turn on the bay lights with the exception of the wet bay. I think we got that taken care of two years ago at the factory. A little comes in around the fresh water hose door.
I left the bay lights on a few times out of concern over the cold. They put out quite a bit of heat. However, I turned them on in storage once and the switch burned out. They had it plugged into 20 amp. There might have been a surge. The only sensible thing to do is provide some heat in the water bay or all the bays. A heavier wire and very small heaters of as many do light bulbs or a lighting fixture or the present light fixture. Plenty of juice when plugged in and furnaces run on the road and if not enough turn on bay lights and or generator if too much for whatever heating is installed.
Not hooked up; an auto gen start...which I keep going to do but haven't got round to it.