I've just bought the Orion Dew Zapper and a couple of straps for my 2 80mm's haven't had them out yet for a test, but it looks a hell of a lot like the Thousand Oaks system, which works very well... If you're handy with electronics, making a PWM controlled dew heater system is pretty easy... I just dont like the finish of any of my home built projects so I went with a commercial one
(lazyness wins 90% of the time)