Normally in early spring and late fall I use a UCO Candlelier in my teardrop, not cold enough to use the catalytic heater, but cold enough (at least for me) to be uncomfortable, for deep winter I use an alpaca wool blanket, which is as warm as a reindeer skin blanket and the coleman pro cat, remember always to leave the top vent fully open to prevent CO2 poisoning.
The candlelier has three candles that last around 9 hours each, you can light one, two or three depending on the heat level you want, it has the added benefit to dry the air, and minimizes moisture build up in the teardrop. I use it between 20 degrees and 40 degrees, if it goes below 20 I use the catalytic heater, it ( Coleman pro cat) has kept me warm down to -10f, and I am sure it will work if I ever go camping in colder weather than that.