-26c, and I was feeling bad about working on mine where it's +22f. One of the previous owners of my coach installed a Proheat XL900 diesel fired boiler. It can be used with the engine running or not, it has an impeller style coolant pump and turns on when the coolant temperature drops to 150f (60c) and shuts off when the coolant temperature reaches 185f (65c). You can read more at
Teleflex Thermal Systems ? Welcome to Proheat.