This is a case I made for the ESP12F 4x relay board, like this one: https://www.banggood.com/AC-or-DC-Power-Supply-ESP8266-WIFI-Four-way-Relay-Module-ESP-12F-Development-Board-Secondary-Development-p-1794113.html

It is designed to just clip closed, so no need for screws or similar. To open once it's closed, you can use a screw driver in the small slot opening to disengage the clips.

This is a really cool relay board that works with esphome (https://esphome.io/), a pretty cheap and easy way to control 4 different things from one device :)

I printed up using 0.2mm, however you should be good with larger layer heights. You may need to use the ‘detect thin walls’ settings in your slicer so that the thin divider wall is printed correctly.