I used a small closet and made (IMO) a good set up using two sheets of 5/8th inch drywall. I cut it on the backside both so it would not break off, (meaning no tear on the frontside where the white is, the corners are even curved as opposed to square)

The other thing it does is to allow it to be placed inside a closet with the white side of the sheetrock facing inwards. That of course both keeps the light in as well as the white provides fair reflection of light. No fans at all.

I use a 2 ft gro light. Florescent even. I take advantage of bringing in fresh air from the crawl space as well as the heat, (what little there is) and the odor (aroma) drift up through and through an opening to the attic.

It's my first and only try at this type set up. I am building a house with a full size basement and will have no need of using a closet......*S*