Furnace using too much propane

Thank you all once again for the suggestions. The one that I am definitely going to check out is the air leak theory especially around the slideouts. It never occurred to me that that could be the issue. I do remember that around June of last year I had to adjust my one slideout. The top was sealed up tight, but the one bottom corner (about 3 feet from the furnace return), had a sizable gap. I did get it adjusted so that it closed up. But I'm sure it was like that from when I opened the camper up in the spring. If the furnace was just constantly sucking in cold air those nights, I would bet that would make it use quite a bit of gas.