So if there was a room in the basement, whose only real air flow was the door, would say a 4"fan and filter in the room with a towel under the door keep the smell from permeating the house?You either need a secondary carbon filter, or you need to dry in your tent, if your concerned with the smell.
As far as HOW to setup the carbon filter, it really doesnt matter. As others have said, you dont need to exhaust the carbon filter.. in a closed environment (be it a tent, closet, room, etc), a carbon filter will scrub the air continuously. The key is to just minimize air exchange in/out of the closed environment.
So assuming your not drying in your tent, and you do get a second carbon filter/fan combo... you can use a cardboard box, yes. You could also hang the buds in a closet with the filter/fan combo running, or just about anywhere else that you can minimize air exchange in/out of the room, while also keeping control over light and rH within reason.
We're moving, and while I have a good idea on my grow space, I haven't quite figured out drying there yet.