I Made this thing not because there weren't any rack mountable Raspberry Pi cases but that they seemed over-complicated or required a lot of time to print often needing supports. This case is simple...it's not fancy but it prints quickly and efficiently and requires no supports.
The settings don't really matter. Should be easy to print on any setting/quality that you usually use. The slicer I uses is Simplify3D and at .3mm resolution with 15% infill this took a little under 2 hours to print. Other cases on Thingiverse often take double that.
The holes fit M2.5mm screws quite nicely allowing you to thread into the plastic. The top cover doubles as both a cover and a way to secure the board to the body.
I used 4 x M2.5 x 10mm to secure the cover/pi to the body