I've got a coleman peltier cooler that I picked up from a friend for free. Like Brian said it's best to make sure everything is already cold when you put it in there. Plus, the reason my friend got rid of it was because he stepped up to an engel because the coleman would drain his battery overnight.

The biggest problem is that they can't be used with real ice since water and electronics don't mix. However, I've taken mine apart and it seems like the peltier is sealed so the only thing than you need to worry about is getting the fan wet. To remedy this I've drilled a hole in the bottom, ran a tube through the wall and sealed it up with silicone. This will allow me to drain the water from the melted ice.

I haven't had a chance to try it out, but I think it should work like that.