Quick question about ventilation/ odor contrl

I built a plywood growbox to stick in my closet that is approx 4x2x6. Right now im in veg under a 400wat MH with 2 5gal dwc buckets. I have one fan in there blowing for circulation and stem strength but no fans for exhaust/odor control.

Im using the daystar AC reflextor right now that has 6" flanges and its just open with no ducting inside the growbox.

Im looking for advice on how to cool the box better. I had several ideas.
What im thinking about doing is ducting the two sides of the reflector out the sides of the box so theres no turns in the ducting, and putting 1 or 2 pc fans in there just to cool the light.

I found a 6" booster fan that does 250CFM for 30 bucks. Assuming it actually does 250cfm, itl exchange the cab 5 times a minute. If i wanted to hook that up to a carbon filter is that good enough or is a inline fan really necessary?

"itl exchange the cab 5 times a minute"

more than enough air flow if the temps outside your grow box are low enough. if you were to put the box in your garage during the summer, like i cleverly have, you will probably need airconditioning.