Fred thanks for your kind words. I'm somewhat proud of my heater (although I look forward to it being improved on or superseded).
"My objective is to keep heating to a minimum to conserve power when running on a car battery", when I'm not on main power I often run off one of the smaller SLA batteries used in burglar alarms etc. Minimising power usage goes up in importance.
I've been using a cheaper temp/humidity sensor in more recent play, I think I mentioned it elsewhere but just in case
http://www.techtoys.com.hk/Components/SHT1x/SHT1x.htm
Somewhat cheaper than the SHT15 (
http://www.sparkfun.com/products/8257), a bit less accuracy but for what we are doing I can't see that matters. There are other alternatives around for the humidity sensing but I've not seen anything quite as neat for the purpose as the SHT sensors.
Bob