Remix of a Couple of Models, put together along with a TPU 120MM O-ring to make things airtight.

Carbon Filter

https://www.thingiverse.com/thing:663864

Hepa Filter Holder

https://cults3d.com/en/3d-model/tool/hepa-filter-holder-for-120mm-fan-86889-style-filters

120mm TPU Gasket (I used Creality TPU from Amazon:

https://www.printables.com/en/model/526692-120mm-fan-gaskets

120MM to 4inch Duct from

https://www.thingiverse.com/thing:6574612/files

Some Amazon Parts I use: (aff links)

Carbon Filter pack:

https://amzn.to/4dPJtsG

HEPA Filter Pack (any 86889 HEPA will work/fit):

https://amzn.to/4dJss3c

Lower Power (Quieter) 25mm Noctua Fan:

https://amzn.to/3yubR3f

Higher Power (louder) 38MM Fan:

https://amzn.to/4bLuM87

DC to Fan Adaptor

https://amzn.to/3wLYniP

USBC to DC (if you want to power it via USBC)

https://amzn.to/3UW6hOP

Bolt kit to hold it all together

https://amzn.to/3KeqLxi