My dry box for 3 - 4 spools of filament.  There are many dry box plans out there.  This one is mine.  
The rod is at a good height for most spools when using a pair of spool hubs on each spool  
1 Sterlite 20qt air tight box.
24 3mmx10mm machine screws (3mm x 8mm will work but I like a little bit of thread sticking out of my nylocks)
24 3mm nylock nuts
24 3mm washers
1ft 3mm OD x 2mm ID PTFE tube.
1 12in 5/16 threaded rod  
I used 3mm OD x 2mm ID PTFE tube because its what I had on hand.
The nut reliefs are too shallow (1mm) on all parts, but they worked for me.
The round base of the rod holder and the U shaped 'extrusion' are perpendicular to each other.  The Sterlite box has an angle of like 3 degrees or so on all sides.  It's not a big deal.  
Loaded several versions of the U shaped rod holder.
m3 with reliefs (m4 hole w/ m3 nut relief.  This one also has an itty bitty section to center the rod.  It makes it special.)
m3 with reliefs dry-ish edition (Same as above but with some added flavor.  It makes it extra…