When I bought my MiSTer FPGA kit, I adorned it with this well-designed case. However, I added an external solid-state drive to my MiSTer, which aesthetically ruined it. So, I made this replacement bottom panel, which holds an inexpensive NVMe drive enclosure that you can pick up from Amazon (link below). Just print it as is (no supports required), and slide in the drive enclosure. The tolerances are small enough that the enclosure fits snugly and doesn't slide around. 

I also used a short, 5-inch USB-C cable to plug the drive into the rear-facing power panel, which makes the setup look neat and free of loose wires. I've also seen some 3-inch USB-C cables, as well, which may also fit.

Parts:

• NVMe Drive Enclosure (Amazon) 
• 5" USB-C Cable (Amazon)

The model in the photos were printed on my MK3S with PETG Prusament, at 0.2mm resolution.