Didn't found what i was searching for - so i modeled it!
As always, first things first - start the print and see whats subotimal.
First of all - turned out -pretty shitty.
Well, had some issues with layer shifting - but all in all - it works for me.
put the screws to fasten it from the inside and tap the print with some nice 3mm threads in the corners. you will then use some nut to tighten it properly. :-D
I have to confess. This thing isn't my best work.
Who the hell needs a 90 degree bend fan reduction?!
Well - me in first place, and i have to claim
My Raspberry now looks really funky!