Congratulations to ChrisV on a nice project!
I hope nobody is offended if I "hijack" this thread - but I was just perusing the JayCar site (that's what I do when it's cloudy, so there's no point in taking the telescope out!), and I came across this project:
http://www.jaycar.com.au/diy-telescope-dew-heater
The parts list runs to a total of about $90 at JayCar (or less if you already have some of the basic components, or shop on eBay):
XC4520 Temperature and Humidity Module: $9.95
XC4454 LCD and Button Shield: $19.95
XC4410 Duinotech Uno Board: $29.95
RN3440 10K Thermistor: $1.75
RR0596 10K resistors: $0.55
RR0572 1K resistors: $0.55
ZT2468 MOSFET: $5.95
XC4482 Proto Shield: $15.95
WC6028 Plug-socket leads: $5.95
RR3264 5W 39Ohm Resistor: $0.48
I haven't done a detailed comparison against Chris's project, and I don't know whether this is a "fork" of his project (or Bob Stephens' 2010 project which he references), but there might be some handy hints for selecting / designing components and wiring, and / or optimising code, for anybody who is thinking of making something similar.