Hey roofus, I keep mine on the floor of the tent. To me, it seems that on the top of the tent, the can gets heat and moisture, which will cause carbon to stop working faster. IMO
But I have had my Phresh filter in my tent for 1 1/2 years and it still scrubs great!!! My brother and a buddy are the only ones that know that I grow and they cant smell anything when they come over. There are some strains that will not care what kind of carbon filter you have!!! Some diesel and kush strains are pretty pungent with filters, oana gel and the wife's scentsy's going!!
Pull your Rhino out and let it air out and dry out for a couple days when you start to germ your next grow and try it on the floor!!!