It gets quite cold in my shop in the winter - I'm too cheap to heat when I'm not in there. I used to bring all finishes and glues into the house for the winter, but that soon got out of hand. So I obtained a very nice refrigerator that had blown the compressor - free for the taking and in excellent condition. I drilled holes in the side, one into the freezer compartment and one into the main compartment. A porcelain light socket with a pull chain was placed into each compartment. I used a low wattage (7 watt) bulb in each one. That's just enough to keep the compartment warm.
I do have to check it every few days to be sure the bulb has not burned out, but bulbs have lasted for many months even though they are on for several months. All in all it has worked out very well. (Sorry the image is so big!)