I wanted a 2x4 mounted spool holder that I could use with a standard 1kg spool and an auto rewinder, and this is what I came up with. It is two pieces that slot together. The countersunk holes are designed for deck screws.

Auto rewind assembly I use can be found in the spool tank assembly guide documentation on printer-box.com (https://help.printer-box.com/home/guide/spool-tank-assembly-guide/4b-autorewind-with-printed-springs-configuration/). The 99mm axle I use with this assembly is a modified version of the axle in that documentation.