wow very nice build. rofl that pile of supplies looks like my floor right now...hahah your build reminds me of mine. I love the square filter..wish I woulda seen that a few days ago before I decided on a round one.
oh, and to the co2 Idea. I would somehome make this box sealed. I have plenty of HVAC experience to break down some sort of a small refridge and figure out a way to cool it internally before I would ever consider the co2, so... Lots of thought and dialing in of this grow before then. I give it another 4 years of pondering and I will have thought something up to configure into the space.