I did have one thought for tempreture controlls..
LED indicator relays, these are set to a certain time and not off load, so adding a varyable resistor where the set resistor for "time on" would normally be you'd get much the same effect as a PWM controller.. just a thought..
Or otherwise how about a thermostatic switch? seems to make allot more sense? seeing as it would react to the tempreture without you needing to pish about turning it up/down all the time.. you'd not even need a controll other than on/off then..
any reason that wouldn't work?