I wrote an article with testing results about this:
https://www.igorslab.de/en/o11d-hdd-cooler-2
This is a Remix of Thingi 4923606, but made to fit the regular O11 Dynamic and not the XL Version.
Two 60x25mm fans fit inside, I suggest using Noctua NF-A6x25
I included the STEP file if you still want to change something.
Print it like shown in my picture, 0.3 Layerheight is fine
To avoid sucking dust into the system, put them as exhaust or use a small filter
The author remixed this model.