This is a case for the common LM2596 DC DC BUCK DOWN converter you can find from all the usual suspects.
It includes a tab to mount to a 2020 extrusion, or anything else.
The top vents also include a small circular cutout to access the tuning pot with the lid on. You can also access all 4 terminals with voltmeter probes as well!
I printed at 0.3mm height and it snapped together a bit sloppy, but without any issues. 0.2mm would work fine.