So I needed a spool holder I could stack. I tried the KUGGIS bin from Ikea, which turned out to be right what I needed.
KUGGIS comes with a hole, so I designed an adapter to fit a bowden tube fitting. A slightly oval ring serves for keeping the adapter in place.
KUGGIS isn't fully air tight, but it's good enough for my environment.
I originally designed it with 6 wheels in mind, but three works as well. Friction keeps the spool of filament from unrolling.
The author marked this model as their own original creation.