This is a mountable box for an RV style rocker switch.

The rear panel is press fit with small "nubs" to hold it in place. Consequently, it is probably necessary to print this at 0.15 layer height or better.

This model doesn't need supports, but the screw mounting holes will end up with some stray filament in it. However you can just trim this out with an x-acto knife and it should work fine.

The screw holes are sized to work best with a SPAX #8 screw. Home depot carries these screws, if you've never tried them, do yourself a favor and check them out.

Tinkercad links:
Box -- https://www.tinkercad.com/things/5R5nXIkdsgz
Lid -- https://www.tinkercad.com/things/9fJoZwdKYvP