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

• fixed some Mesh Errors
• removed two now unnecessary holes for screws in the case
• increased the width and length
• decreased thickness of the interlocking part
• moved a few things around to make it fit the O11D

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