Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4755983.
I bought a buck converter to go from 24V to 12V for quiter fans. I looked for a case here, but didn't find fitting ones. Didn't searched that long though.
To get a little bit more into designing things I made my own housing.
My buck converter has the dimensions 50 x 25 x 14 mm.
The case has ventilation holes on top and bottom as well as on the sides. The converter mounts without tools as it is held with minimal play by the case alone. The case itself has four mounting holes in a 40x40mm grid, because that is suitable for my printer. I dimensiond the holes to be big enough to melt M3 threaded inserts into it. But of course you can just use nuts and bolts or cable ties as well.