I saw somewhere else that people recommend using this one from Amazon.

Personally, it's still a big metal box, just in a different shape. I instead modified my PSU so that it only has the six 12v wires coming out of the box, plus the green wire jumpered to negative inside the box to allow it to run. I printed a (non UL-listed) flange for it (but then had to hack the top part a bit to get the big fan to work).