My first grow cabinet using cfl lights and antique freezer

Late last night i decided to do a little work on my box and found that the extension cord that was hanging out the front would in fact fit through the hole in the bottom with a little bit of triming of the plug. It looks like a very clean cabinet now and is completely light tight. I plan to get a fan and install it to the back since the metal inside seems to hold heat very well. As far as circulation of air goes it is great.

Isnt there some sort of organic material that releases co2 for the plants that is cheap. I thought it looked like moss of some sort. Maybe toss it in for added support.