Hi Matt
I use the Kendrick standard dew heater system which consists of a controller and 4 sockets for heater strips. I have found it to be completely effective and reliable in the 5 years I have been using it.
I have heaters for a C9.25, Vixen 30x125 bino's, Vixen 4" refractor and a number of 2" and 1.25" strips for eyepieces and camera lenses.
The controller is powered by 12V from a mains adapter although you can use a 12V battery. I have the Mk IV controller which was designed not to affect ccd imaging via EMI/EMC and it has worked so far with my ST7E ccd camera.
The controller has a continuously adjustable rotary knob from off through Min to Max and operates on a 40% duty cycle. The lens / mirror needs only to be 0.5 deg C above ambient to prevent dew build up so I have never (yet) experienced seeing problems.
It is an expensive system but so is my gear and I chose it because I wanted a reliable system that would not let me down at remote astro-camps.
I would be happy to answer any further questions you may have.
Cheers
Dennis
PS Here is the link to the Kendrick site
http://www.kendrickastro.com/astro/dewremover.html