Before the computers could be mounted, control boards were attached the PCB holders. These were previously populated with components and Arduinos. Each control board had to be strapped in place with a long zip tie which went through the top of the PCB holder. The Raspberry Pi will be covering this area so the zip tie had to be installed before the computer.
The Raspberry Pis were installed with #4 (3mm) screws which passed through the computer mounting holes, spacers and into the designated holes modeled into the PCB holder. The clearance provided by the spacers was more than enough for the zip tie underneath. The space should also aid in keeping the computer cool since it is open on all sides.