I 'm going to construct a grow box from an already made cabinet or dresser. My main concern is air flow and co2. Can I just rig up a small fan? How would I provide co2 to this box with out breaking the bank bc I am trying to save as much money as possible. This box will be for auto flowering plants only so they will stay small.if I'm lucky just 3 plants at a time. Does co2 need to be provided for such small plant life if air flow is good? I will be growing in soil. Thanks.