Self-tapping M3 mounting holes are spaced 45mm apart.

Print settings:

Material: PETG

This is important.  PETG is the only material with the right mix of rigidity and flexibility to clamp onto the DIN rail solidly, and also be easy to remove without being too stiff and needing a screwdriver to pry it off.  I hate PETG, but for this project, it really is the only right choice.

Wall thickness: 3+

Infill: 30+

Seam: Sharpest corner, Hide Seam/Smart Hiding

The main place to check is that you don't want any seams located on the thin wall sections that form the flexible latch on top.