I live full time in my 30.5 ft Prowler 5th wheel.
I live in Carson City, Nevada where the average temperatures since November has been 23 at night and 45 during daytime.
We have strong winds most days. Some gusts are 100 mph coming down off sierra Nevada Mountains. Local RVers refer to those gusts as "Pucker Winds".
I keep the thermostat set at 68 all day and night.
I cook with the gas stove every morning.
I run the water heater on propane only.
My average daily propane use is less than two gallons per 24 hr day.
However .... my monthly cost has over doubled this winter... from $1.25 per gallon last winter to $2.94 this winter..
The reason I included this information is because I think there must be something wrong with your heating system .. either that or you live in North Pole...
I suggest having it checked out by a licensed RV repairman.
Best of luck,