This is a remix of the Stackable Keycap Storage Tray by SpikedSynapse. 

I made the trays wider to accomodate a full row of F keys next to eachother, so you can fit 12 units of keys in a row. 
I also made a taller version available for taller keycaps like the SA profile.

This tray will still fit on an Ender 3 bed, but only just. You can use the same settings as recommended by SikedSynapse, just make sure to slice in Cura.