I use an old heating pad for mine. It works just fine. My garage recently has been in the 30-40 range, and I have had no issues keeping my fermenter at 68.
If you got the digital Johnson Controls temperature controller, it can be a pain in the spring/fall. As stated before, it is not a two stage controller. It supports heating and cooling, but not at the same time. You have to take the controller apart and change the jumpers around each time you want to switch between heating and cooling. I have one that I used a couple of times for fermentation, and now it is on my keezer. I replaced it with the STC-1000.
For the time being, I just run the cords between the door seal and the fridge. I just shut the door on them and have had no issues.