This is a modified version of
https://www.thingiverse.com/thing:3033216
to suit the Raspberry Pi 4 B, which has a different port layout meaning Pi 3 cases won't fit. I've also added an additional opening in the lid to accommodate the PoE hat, with a small amount of strengthening due to the opening location.

0.2 layer height works well and support is required under the 2020 rail but no where else. I printed with 20% infill but it doesn't really matter as there is very little infill.

19/05/20 - Added a lid to enable mounting of a 30mm fan.

Print instructions

0.2 layer height with support under the 2020 rail, I printed with 20% infill but there is very little so it won't make much difference.