This comes in 3 parts depending on configuration needs. All configurations allow air flow for cooling.

The Base Mount can hold a HDD that can be easily swapped or a permanent SSD installed at the bottom. Base Mounts can be stacked and held together (I used 3M x 12mm screws and nuts to minimize vibrations).

The Middle Mount can only hold a SSD but can allow rapid swap out. It also leaves enough space to install a SSD at the bottom.

The Top Mount can only hold a permanent SSD.

Recommend purchasing thumbscrews 6-32 x 5 for securing drives.