I love this spool holder (Big Thanks to the original designer!)
Main features are:
 1. Spool holder (obviously)
 2. Dry-box (you can add desiccant)
 3. Buffer (no need for fancy buffers, it's a tight enough fit inside and the filament just stays on the spool when it is being pushed back by the extruder)

You will need:
PC4-01 pneumatic fitting with 10mm thread x 1pcs (designed for it because it was the one that I've had laying around)

I have applied one thin layer of clear coat(spray paint) on mine just to make it a bit more moisture resistant.
I never used the gasket because my direct drive printer has too small of a build area.