With the front plate designed I had more or less clear what the bottom plate should do:

* It needed to hold the front plate securely. I don't plan to remove the thing often but if I need to do maintenance I don't want the thing falling apart inmediately.

* It needed to be compliant with the CD-ROM specifications, regarding measurements. The microserver uses a non-standard rail system so I could not just drop something with the same size. The screwholes in particular should be within the specs regarding position.

* The CD bay contained a 2.5 inch SSD. The bottom plate needed to keed the drive secure inside

This is what I got

After an excruciatingly slow 10 hours of printing i got this:

The base slid in and out nicely, and the hole allowed the USB cable to pass through nicely.

In a future design I would make the drive guides a bit taller, and also add a back limit so the drive is easy to align with the pins that keep it in place.