Here's a link to the DIY mini-fuge made out of an AC500. I made mine out of 300s but same principle.
http://www.fishforums.com/forum/diy-do-yourself/5705-my-diy-ac500-refugium.html
http://www.fishforums.com/forum/diy-do-yourself/5705-my-diy-ac500-refugium.html