We went camping last weekend. Day time temps were 48 degrees the first day and 58 degrees the second day. Night time temps were 30 degrees the first night and 36 degrees the second night. I filled the propane tank before the trip and used 1/8 tank (56 pounds/13 gallons) of propane running the heater the 2 days.
We were in the camper most of the day the first day and the heat was set to about 70 degrees. The second day we were out for about 8 hours of the day and the furnace was off. My wife is cold in GA in the summer, so the thermostat is usually set to 68 at night. She still uses an electric blanket.
Like a few others have said, it sounds like your propane use is normal. I agree with the others that getting electric heaters and keeping the thermostat down lower would help conserve heat. However, the furnace still consumes about 1/2 pound/hour no matter what temp it is set at. Keeping lower just keeps it from running as often.
-Michael