I used the IKEA 365 10.6l box and mounted a rod inside that holds two filament spools.
I designed a very simple mounting bracket for the spool rod, that can either be hot-glued or skrewed to the side (I used hot-glue, and it holds well - but I also included 4 holes to srew on just in case…).
My rod diameter was 8mm, but the model is fully parametrizable in Open SCAD, so you can easily change the diameter to whatever rod you have available.
The author marked this model as their own original creation.