I can recommend a 4 Channel Dew Heater controller from Thousand Oaks.
Allows adjustment of 4 different heaters and has a 12V port as well. I run the Argo Navis of the dedicated 12V port.
Very handy.
http://www.thousandoaksoptical.com/w...ducts/dew.html
I think Star Optics are the agents.
There may be some other more locally made controllers around.