edit for anyone new still coming across this design & hoping to use it alongside other prints that would clip on to the X Gantry cover, I've uploaded a new take on this original design which effectively replaces the gantry cover on the  Ender 3, adding the Octoprint Monitor while still allowing you to use other designs such as clip on camera mounts etc which can be found Here
Update 21/12/2019 - Added file OctoMonitor_Mount_v2.stl, I have increased the width of the slot for the Wemos board by 0.8mm to more comfortably fit the v3 revision as requested by donsadlerjr in the comments and uploaded an updated step file. As mentioned below the initial file does fit the new v3 Wemos Mini however the tolerance is very tight so getting the board out again proves difficult unless you break the printed part, I personally preferred it this way as stay put when unplugging the USB cable.
Just a simple clip on case for the  Ender 3 X gantry to house my Octoprint Monitor. I just wanted a quick way to check on my print status…