Hi,
I've tested the tank heater to -27 C with no other source of heat (i.e. RV not heated in any way, just the tank heater active), using 100 watts from a fan based heater. It would be easy to add more wattage should that prove necessary. There will be at least some radiant heat from the interior of the RV.
The fresh water tank is within the area heated by the propane furnace.
Salvo wrote:
As I see it, the tank heaters will be overwhelmed. They will not be able to keep the contents from freezing. He'll need to keep all the tanks dry.
Sal