Why I did this:

• Dasfilament.de overfill their #MasterSpool refills to 850g (they still deliver the best refills I know, though).
• A freshly refilled spool thus is in constant danger of filament jumping over the edges.
• Both Mark Rehorst and Graham Watson have already designed spool holders, that could prevent it. (I had to invert Mark's concave roller concept - as mentioned, my spools are overfilled.)
• IKEA now has cheap, airtight containers (365+ 10.6l / 11 qt, No. 103.930.64, the Lid is No. 303.930.63).
• The IKEA container can accommodate two #MasterSpools or regular 750g ones (e.g. the Häfner SD200K used by Innofil and Formfutura).
• Squeezing those two spool, held by individual Anti-Tangle Spool-Holders into one of those 365+ Dryboxes required a new design.

Drawbacks:
- RichRap din't design the #MasterSpool to run on the edges (where the "elephant foot" is located) - you'll have to properly deburr your spools.
- There is no room for "rechargeable" de-humidifiers. But using "darkytoothpaste's silica gel bottle" (https://www.thingiverse.com/thing:2763602) inside the spools, combined with collected desiccant from various bags, works for me. I regenerate the silica in the Microwave oven.

Inspiration:

Mark Rehorst
https://drmrehorst.blogspot.com/2017/11/3d-printer-spool-holder-design.html
https://www.youmagine.com/designs/filament-spool-holder-for-3d-printer
https://www.youmagine.com/designs/improved-spool-holder-design-to-prevent-filament-tangles

Graham Watson
https://www.thingiverse.com/thing:2479238

A. Ozen / Sp4wN
https://www.thingiverse.com/thing:3320749

...and of course RichRap:
https://richrap.blogspot.com/2018/01/masterspool-proposed-standard-for-3d.html