Hey Justin, I think I said that the units are 40w each. Your single one is 72w and is the better unit to have. I did mine on the cheap, but yours is the better way of doing this.
Large heat sinks certainly are the way to go, both mine are 4" square or there abouts, they remove the heat really well. However I could increase the efficiency of the peltiers with increasing the current up to 14 volts rather than using a 12 volt rail. Also fully covering the rear back will increase the overall efficiency too. I currently have the fins exposed but have built up the foam layers to be level with the tops of the supporting fins.