In a closet, a fan blowing out of the door won't be adequate ventilation...or people wouldn't even waste their time with all the ducting and extra measures of evacuating air. Those bins aren't that expensive, you're better off grabbing another and setting up your box now...also putting those plants in that box and not having a top on is letting more light escape than you think. If you have a top, you can use a material to reflect the light back onto your babies and make them grow even better. However, if you are set to continue growing the way that you are, you might want an air conditioning unit in there. Even if your box is well ventilated, you would have to move it to a cooler room because it will still have issues being surrounded by a hot closet with stale air. So I guess you have some thinking to do! Let me know if I can help, and be sure to post what you come up with! I'm smoking all night and camping on the forums lol.