Usually, I use the controller from the "Cheap eBay Temp Controller" thread. I believe it is an aquarium temp controller. I have also used my dyi Arduino temp controller.
I have held a five gallon Better Bottle at 100F with the eBay Temp Controller for the lactic fermentation of a Berliner. I set the range of the controller at 1F. I used 2in blue painters tape to secure the corners of the temp wrap to the Better Bottle. I taped the temp probe under a piece of reflective bubble insulation and then taped the insulation to the side of the Better Bottle. I put a sweat shirt over the entire thing. I think it ran at about 60% duty cycle.
I wish I had pictures. Let me know if you have more questions.