Last year I replaced the broken GD-ROM of my Sega Dreamcast with a GDEMU. While it works great and does everything as it is supposed to do, there is a large open space where SD cards tend to get lost:

Twistedsymphony developed the design of a tray that closes this space and also adds slots to store 4 or 5 SD cards. Design and instructions can be found on Thingiverse. If you don’t have access to a 3D printer then you can use a printing service, e.g. (3D) Hubs.

I chose the 4 slot base and had it printed with 200mm black PLA, this is what I got:

Base and shield fitted underneath the SDEMU and into the top cover:

The open space is gone: