Greetings!  This system makes use of all those Pressure Advance towers from the OrcaSlicer filament calibration regimen.  
 

Just glue the caps on the bottom side (side with the split on it for me) and then leave the upper cap (tapered lip) loose.  The trays can be stacked vertically, by printing four legs and gluing as desired.  Tapered knobs on the legs fit recesses in the trays.

Tolerances are fairly tight for the lids, so if you are trying to use a tower for something like ABS, you'll want an ABS cap.