I got both of these of this site but I'm to lazy to look for a link
The first one is some wire wrapped around a 6" stove pipe connector with a 6" cap on the other end. Screw the wire to the cap & connector & wrap with a filter. I suppose you could rig up a cage inside the wire & fill it full of carbon.
The second one is activated carbon poured into a breathable seal able bag. The guy who did it used scotch brite towels & stitched together. I could not find them so I used a wool lite laundry bag. It's way to big but I just stuffed the extra in the pipe, just make sure air cannot get past the carbon. Again I used a 6" stove pipe & wire.
I can't say that either one will work but right know I'm using the second one. My room hasn't started to stink but I should be finding out in a couple of weeks. The guys on here who built them seemed to love them.