Where To Put Odor Gel For PC Grow Box?

Quick question forum, where do I PUT the gel if i'm using PC grow box? The out vent is on the TOP of the case where the Power supply used to be. Should i put the gel IN the case or on TOP of the case or right in front of the outtake or right behind it etc etc.

Thanks
Mr. Rager

I would put it on the outside of the exhast fan(Air going out), just make sure to somehow seal it so the odor doesnt exscape.