You went camping, with an empty fresh water tank?
Expecting to use campground water!
Just to save a few pounds you're weight?
Always travel with at least 1/2 tank
That fresh water has saved more than one radiator and engine when traveling, and a real convenience if stuck or stranded because of bad weather, road accidents etc..
You have the cat heater and the electric heat,
You can trouble shoot the furnace at home
Don't forget to check your battery voltage
A bad wire connection , low voltage, and the heater won't work correctly