You could use a hooded or stopper thermowell:
This way you're reading the temperature of your actual fermentation, which can sometimes be 7-10°F above what the outside / ambient temperature is. If you have it set at 68°F but you're actual fermentation is 75°F, you're going to get some ester production (depending of course on the yeast strain used). Just a thought...
EDIT - If you're just using it for kegging / dispensing, the temperature won't fluctuate because you're not fermenting anymore (obviously..!)