This is a remix of the Resin.io STEM case. (https://www.thingiverse.com/thing:2275029) I made the top solid (no cut-out for the GPIO). I added standoffs to both the bottom and top where there were none. I added a lip on the top so it just stays snapped shut with no glue.
I printed on a PowerSpec Ultra with PLA at 25% but it should be fine with much lower percentage. I'm also using 3 shells but just for durability.