I have now finished fine tuning this design and it appears to work well. There are two filter versions, one for pad filters and one for holding activated charcoal. Using it with either filter type and either orientation seems to work fine.
This print takes 24 hours with my settings for the main body and about 3-4 hours for each filter part. Only the part with tab overhangs requires support. For my Anet A8 printer it uses the full bed width, if your bed is smaller you may be able to scale the parts down a bit.
There doesn't seem to be interest in other fan versions yet so I won't do that version unless I hear otherwise.
Good luck if you decide to make it and feel free to ask questions.
This was inspired by this one...by "nrp"