Karl what size Peltier are you using? Size in mm and current. The newer heatpipe copper heatsinks are far better than plain vanilla aluminium. Here is one that would fit nicely on the back of a DSI and would work well without a fan.
The controller you mentioned sounds interesting. I need to control about seven or more amps to get a constant temperature in the fridge.
Here
http://www.pccasegear.com.au/prod5602.htm
Bert