This is a a small box which I have designed in Fusion360 for my own version of the DIY Atari Punk Console (Sound Synthesizer), with tone, pitch, 4 filters, audio out, CV in, on/off switch and standard DC connector outlets.
It uses four M3 screws to secure the lid and there is a bit inside of the box for securing the PCB. Admittedly, I really should reposition that, but I could not be bothered to do it so far.
You are free to modify it or use it as it is for your own personal diy projects if you wish.
If you are interested in the schematics, assembly instructions or what it is doing etc. See it on my blog https://apcreative.space.
I use brim for support to prevent corners accidentally "curving up". You most likely could get away without it, but a bit of brim cannot hurt...
Use your preferred infill. The wall of the box is not thick (2mm) anyway. I have used 50% infill for rigidity.