Are you stabilizing temperatures for beer fermentation or simply for storage of beer that was already made?  I've considered going with a Peltier for my fermentation temperature control, but I've got concerns over efficiency.   We've had 5 gallons of fermenting beer spike up to 11 degrees on the first day or so.  Just curious how hard your Peltier is working.  The reversibility of the Peltiers is HIGHLY temping.

This project is just for bottle storage. I have had a fermenting cabinet in the back of my mind and the Peltiers I can afford simply can't do it. The amps required is not realistic in my opinion. 

I've been relying on thermal mass to keep the temp from skyrocketing during the initial fermentation phase.  I figure placing our 5 gallon fermentation buckets in 5 gallons of temperature-regulated water should get us close to knocking the temp rise in half (give or take).  The problem with that is our sealed fermenter box becomes a humidity swamp.  If you are looking for super-stiff regulation, it's going to take some SERIOUS oomph to fight off that temperature rise.  I'm content with snubbing that peak a bit.

I have had a PC water cooling circuit going for a while now, again it just was not getting the job done.  However when I mounted a long  scrap of  1mm sheet metal to the radiator all the beer cooled off in a hurry. My take from this is that I need more air flow passing the radiator to get enough effect. The problem with the sheet metal is that it cools the beer but the not air... and thats where I can read the temp.

Warming up is not an issue. 

Cooling down as expected is difficult. I can drop the temperature 5-6 celsius easy... but thats when the room outside starts warming up... the warm side of the Peltier and the pc power source and well the cool area stops dropping. I believe this can be solved simply by venting the backside of the Peltier plate direct outside... but thats too much work and I will be revisiting this later.