It is always easier to control temperature (or humidity) in a smaller and confined room or even closet. I use heat lamp of 60W in a smaller room at a distance of 4 feet away from the containers. Try to keep your containers away from the wall facing outdoor and allow sunlight through your glass window in the afternoon to create a "green house" effect. Close the window with curtain or blind at night and switch on the night heat light if temp gets too low. I also have a little fridge of my own (yep, my "Boss" doesn't like any insects in her fridge) that helps warming up the place too, and i have my study room next to the wall which have computer CPU running almost 24 hrs a day. But don't neglect humidity as all these heat will dry up the air.