I use a small heater in my wet bay to keep everything warm and two ceramic heaters inside the coach with the propane set at 60 (just in case the others fail)
i also just put my water on board ilo hooked up.
i don't hook up the sewer until I am full ...dump ...then unhook...
I have had no issues even at 10 degrees doing this
Just make sure the heaters have safety switch's.
Hope this helps.