Gregory's Server@libreleah I had a similar issue a few years back for my custom SteamBox 360 build. With a decided lack of access to 3D printing I just cut a hole in the side panel and put a custom fan grill on it.
(Yes, the internal dc-dc power supply converter thing is still held on with a zip tie to this day.)
@Unaccounted4 This looks great!
Alas, the chassis on my machine is *solid steel*. I actually can drill it, but it gets messy. And it's physically difficult. I'm sweating; I'm in the process of doing it on mine, as a test, to see if it improves temps. If it does, then I'll start designing that custom case.
OR:
Use some sort of automated drill, that can drill precisely in a row (without me holding it). Then I would drill the default chassis (and clean up, paint it and put a dust filter over it)