I picked up 3 x 12-24 volt 8 Amp motor controllers for $14 from DealExtreme. Got them to manage my cooled 450D TEC unit. Didn't thought of using them as a dew heater controller unit. I have a 12 volt supply with about 12 amps deliverable and several other options in power supplies plus various heater element options in Resistors, Nichrome or carbon film possibly.
I can feel another project coming on.

Cool !
Currently I use a 6 watt beer brewing mat around the Lunt just behind the objective. But it's in the Ob at home so 240 vac available. I wrap an old hand towel around it to insulate it. Works well.