Well, my experience has taught me that airflow will do a lot more to evaporate water than heat. So, to get your boots as dry as possible, try using a little forced air instead of heat. The best way to accomplish this is to just grab a couple of case fans and an old AC adapter that outputs 12 volts.
Step 1: First Connect the Wires
Step 2: Plug It In, Stick 'em in the Boots
Try to place the fans in such a way that you can feel air escaping. These will have the boots dry as a bone overnight. They also work for shoes, hiking boots, xx boots, and any other wet footwear you might have.