man as far as ventalation I had a big prob with my 400MH and still do. Im 9days above soil and the first day my temps reached 109 with the growbox shut. I have a box 4x2x7, so I had to leave the growbox door opened which werent my intensions at first. So as far as a 400MH its super hot unless you have a really cool room. I would suggest YOU RUN A TEST first. See what happens with in the cabinet B4 you put the plants in and get a few CPU fans in there to blow fresh air inside (bottom) and few fans to blow hot air out, from the top :thumbsup: good luck. My plants are doing fine now but I still need Fresh cold air to blow inside. If I knew before hand I wouldve run a test 1st!!!!!!! :thumbsup: