Second version of my first Pi3x case. Here : https://www.thingiverse.com/thing:3324451
The board sets high enough in the case that a side fan will cool the top and the bottom. There are two top covers. One with a fan and the other without. Run 1, 2 or none. Your choice. With heat sinks on all chips and 2 fans all mine over clock to 1.5K with no issues. Heatsinks are a must*
Try at your own risk, YMMV.
The covers snap on well and stay in place. Any issues let me know.
This was designed from scratch using Tinkercad. I get a kick out of see how complex of projects I can do. This was simple.