This is my (I guess) final solution for (mostly) Bambu PLA spools, 20 spools fitting into that IKEA Ivar shelf insert, maybe you get some inspiration from it…
I used Bambu Labs Spool Stand by Roman as the base, and added braces to ensure even spacing and some stability. There are two Sunlu and two Eryone spots, because the braces added just enough width so that 5 Bambu spools don’t fit any more, and the other brands have smaller spool widths.
Where I live I think for the PLA I can go without all the keep-dry magic treatment (I dry my spools after unwrapping, once), and the more delicate stuff is in a container with desiccant etc.