I know this is late, but some more details might be helpful. Are we talking about an electric/solidbody guitar, or an acoustic? I don't know about acoustic guitars, cuz they seem like their own thing, but with a solid body guitar, I imagine a wide chisel to get the walls straight, then sanding by hand with increasing grits of sandpaper to just clean up the surface finish. One of those sanding sponges might be helpful.
Not at hand, but they are 1/2” plywood with simple routed grooves on hardwood runners. Two of the three have little 3d printed, scalloped pen “trays”. The third is deep enough for most brands of 50-60 mL ink bottles.
The back is just hardboard set into a rabbet, so this thing looks neat against a wall. It’s also heavier than it looks, lol, and with plenty of, umm, “character”.
woodworking
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