This is a minimalist box for those ubiquitous 5V and 12V relay modules (example on Amazon).

There are two versions of the base - one that uses M3 screws (threads are modelled so should print), or a tool-less stud version.

The lid simply presses on - there is enough friction along the print layers to keep it on.

The slots are there to see the red power LED and the green relay active LED rather than for ventilation - there's nothing that gets really hot on these boards. My workshop gets full of sawdust, so I try to limit dust-gatherers where I can.

Note that if you use the stud version, the fit is tight. You're unlikely to be able to get the module off the base again without breaking a stud or breaking the base once its on. I wanted a firm hold - it's a one way trip, baby!

If you use the M3 screw version of the base, the option is to use two screw holes to mount the relay, and two to mount the whole thing to whatever it's going to live on. I just use double-sided tape. (Huzzah for double-sided tape!)

I printed in PLA, 0.2mm layer height and 15% infill.