The side pieces fit into the base and should be secured by hot glue or adhesive.
These files can be edited with software like Tinkercad, Inkscape, or any other SVG editor.
24x12_set.*.svg : A full print set of the pieces needed to make a single rack on a 24x12 inch piece of material.
18xside..svg + 4xbase..svg: By printing 2 of the 18x and 1 of the 4x sheets, enough pieces will be printed to make 4 racks (enough for 16 RPIs and devices).
base.*.svg : The base piece. Has holes enough for 4 slots.
side.*.svg : The side piece. Fits into the holes in the base. Has slots cut out for better airflow.