In this one I used a 1/32 DIN proportional controller from Auberins.com. The sensor is a RTD-100 thermistor I got from them as well. The box is the same type used in the ON/OFF controllers in the other post.

I used a small PC-board mounted SSR in the box. The current rating is only 3 amps, so I fused this unit at 2 amps, which is more than enough for heat pads.