just got another 4" duct fan and I'm going to use it as a second intake ( two 4" intakes.....One 4" exhaust....all 3 80 cfm) Before I go through all that though I'll try shutting the intake down and adding a small fan inside the box.

As far as my setup goes.....the closet/grow cabinet is in my bedroom that is cooled by an in window AC. I am venting out of the top of the box into my bedroom. room temps are around 70 at all times.