Stuff insulated pillows into the ceiling fan vents to block heat from escaping.
Insert Reflectix between the blinds and the windows to block cold air from falling onto your beds.
Use BOTH a small electric heater AND your propane heater. The electric heater is better at maintaining steady heat within a narrow temp range, but won't prevent large steady drops in temp. The propane heater will handle the big drops in heat but is terrible at maintaining it within a narrow range. If you only use propane on a freezing night the temp can range 8-10 degrees.
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