This here is the dry box I used for my very first grow a while back. It measures 31" x 21" x 12' deep. I first used it to quickly hide my plant (which was in early veg and was during the dark cycle) from an unexpected guest lol. I just wanted to quickly place it over the plant without disturbing it. Worked like a charm. Anyway, after removing the box, I decided to just use it as a dry box as well. I made the holes, slid some thin rope across the inside top twice, made a tight knot, burned the tip of the knot a bit and did the same for the one middle rope. Since I was growing just one plant, that’s all I basically needed. Then I placed the box in a very dark corner of the room I had prepared for it. Now I just hang them to dry in the same room I grow them in. No box needed.
As far as fans go, I didn’t want my buds to dry too quickly, so I had a very small fan hitting the walls, which then just barely reached the buds. You have to feel them every day to make sure they’re not drying too fast though. If they are, then either move the fan away, turn down the setting, or turn it off altogether. I guess it also depends on how many buds you're trying to dry. A couple of plants I guess a small fan to no fan will do. If you have good air circulation in the room you're drying them in, then you may not even need a fan. Large quantities of buds I'm guessing may require a fan or two.