I, too, use heatsticks - 2 110watts ones that I use on outlets near the washer and dryer in the basement; I'm on my second set. I'm pleased with them and am able to brew all year long, even during snowstorms in the warmth of my basement.
I did experience carmelization (or at least, some sort of buildup) on the first set I used that really did not affect the beer until the buildup started to flake off and leave a burnt taste - just at the time I started to enter competitions. I started to have moisture problems and had to build new ones.
With the new ones I have been able win awards with Blonde Ale (one year after making them). I have been wiping the heating element to eleminate any buildup. Anytime now that I have a major buildup, it has been when I brew a wheat beer which fortunately I do not care for.
Now here is my problem: how to build a simple PID controller. Are there any plans available? I am not an electrician and the beauty of heatsticks is that they are so easy to make and use.