A simple base and lid to turn the core of empty Elegoo cardboard spools into useful containers. The base locks on to the inner and outer wall while the lid only holds the outer wall. I have included the step file so adjust and mix to your hearts content.

Preparation:

Remove the sides from the empty spool, they pull off easily by hand. Remove the hard glue from the 2 ends using a hobby knife or deburring tool. You could lightly sand the ends clean but it is not needed. 
Assembly: Slip the spool core into the base, place on a hard stable surface and press down until you feel it engage at the bottom. The lid sips on and comes off with a little bit of twist and pull.
 

Some of my cores measure a bit larger than normal so that would require a small scale up in the slicer if you want to use the slightly larger ones. I just feed the cores I use for containers to my wood stove to heat the house.