I like the dry box design descended from tcosta's design but I don't like the way the spool holder has to be bent open and the spool slid in without snagging.   So I designed this one with an axle. The spool can be dropped in vertically and  popped out by pulling up.  It does have the possible drawback of not allowing the dry box to be turned completely upside down (at least not if there is much filament on  the spool).  

Its probably not obvious from  the photos that this uses an over-center design that grips the axle and requires force to push it in or pull it out.  This is the second of two designs and probably the lesser one. This one requires no hardware and is 100% 3D printed; but you must be able to print in TPU and ASA.

The pincer must be printed solid in a flexible material .  Use 400 walls or something rather than 100% infill.   I used 95A TPU and I think the flexibility is critical to the proper functioning.  Likewise, I suggest you don't substitute for  ASA in the springs.  The springs need a low-creep material and every different filament type I tried needed different tuning.  So stick with ASA.  Note the way the springs are oriented with the slightly curved  end attached to the center piece  and the loop going up next to the center.

For parts like the frame I much prefer square nuts.  If you don't want to use them, hex nuts will work in a pinch and you could still use heat-set inserts perhaps with a little drilling

It is designed to grip an 8mm x 87mm rod which will serve for spool holders using 608 bearings.  It also works, less well, with 5/16 inch dowel rods etc.

The frame will fit the dry box bases mentioned above.  

Finally, this type of spool holder can have problems with filament unwinding and coming off the spool.  The tensioner, printed in TPU, can snaps onto the frame when needed. It lightly rubs on the spool to provide slight resistance to the spool over spinning.
 

I really like this design but getting the right balance of forces is so critical I don't know if it is suitable for sharing.  The parts are designed down to the tenth of a millimeter -- necessary to get it to work reliably.  It may be that these parts only work printed on my printer with the exact brands or manufacturing lot of filaments I used.