There are two versions of the body, one for the right side and one for the left.  Due to the modeled threads for the PTFE connector, mirroring may not work since the threads will be reversed.  A left side version is available as an STL.

A STEP file of the entire assembly (right side version) is included should you want to remix for your specific needs.

Hardware

• One PC4-M10 PTFE tube connector.
• Two 3030 drop in t-nuts.
  • *shameless plug* If you need a couple t-nuts you can print and use this:
    https://www.printables.com/model/10424-m3-drop-in-nut-for-3030-extrusion
• Two M3x10 or 12mm bolts
  • Round head would be best but socket head caps will work.
• Hygrometer
  • I use the ones from this link in my filament storage boxes and converted dehydrator. They work fine.  I see the rectangular ones used a lot but don't have one to design to.
  • https://www.amazon.com/JEDEW-Thermometer-Temperature-Humidifiers-Dehumidifiers/dp/B07GR65CNT?th=1

Installation

• Thread the PTFE connector into the filament exit.
• Temporarily remove the spool holder you plan to install the drybox over.  The spool holder end will not fit through the square hole (a square hole, round peg dilemma :)
• Attach the body to the vertical extrusion using the t-nuts and m3 bolts.
  • If using “roll in” t-nuts, place them about 105mm apart
  • To install the drybox as high as possible insert the top t-nut into the horizontal extrusion.
• Reinstall the spool holder through the square hole (dilemma solved!)
• Slide the cover on then clip the cover with the… wait for it… …CoverClip.  More seriously, this clip was added after printing the first prototype and finding the cover left a small gap at the front, probably from a bit of warp induced by the rib on top.

Feeding Filament

• Disconnect the appropriate PTFE tube from the side filament sensor and route it into the PTFE connector you just installed.  As a bonus, this smooths the bend going up to the extruder nicely.
  • Make sure to either disable the filament sensors from the printer menu or just trick it with a short piece of filament through the side sensor.
• When loading a spool I find it easiest to feed the filament from the box into the PTFE a little bit then install the spool completely.  Next, disconnect the PTFE from the box and feed the filament from there.  Once it's fed a country mile (1.6 country km) to the extruder, reconnect the PTFE.  Honestly there is really no great way but it is certainly doable, and simple after the first time or two.

Notes

There may be filament routing issues on the left side where three spools call home by default (my setup).  I have not installed this on the left side so cannot say how this will or will not work with three.  Pretty sure three of these will not fit on the same side.  Maybe two and one open spool would?

I know this box isn't technically “air tight” but even without the clip and only a few small bags of desiccant, the hygrometer dropped to 10% (it's lowest) and stayed there until I opened the box a couple days later.  Just make sure to dry your filament first, especially if it's on a cardboard spool.

The ones in the pics are printed in PLA but any material should be fine.

Hope you find this useful and, as always, Happy Printing!