I needed a tray to hold whiteboard markers, cleaner and an eraser. Searching didn't turn up any one thing that did all I wanted, so I created one. This was designed to mount with hidden fasteners, the back of the tray has a tapered dovetail, and there is a second part that is meant to be screwed to the wall. The wall mounting part should be printed standing upright, but upside-down to prevent the raised edge formed on contact with the print bed from interfering with the fit. If the fit is too tight, try scaling that mounting part up by 1%, or if it is too loose, scale it down.