Ken,
In my first trial I did take the peltier from a car fridge. The problem I found was that it was physically the same size as the DSI case. This meant that there would need to be more "fiddling around" to get good contact between the cooler and the metal case. By using the Jaycar peltier, it was smaller, lighter and hence easier to fit.
I just connect it up to a 12v power source and let it run without temp control. As I mentioned in the original post, a series of darks may need to be taken each time you go out with it, but after 20mins of "cool down" a single frame at each exposure setting is fine.
If you can, get a Mogg adapter and connect slr lenses to the DSI. It works really well.
cheers
Mark