Not really needed these days as Martijn's wooden holder that comes with the Ultipanel in my opinion blends seamlessly with the Ultimaker.
However it is still good for those that like their additions to be of the printed variety.

The circuit board just push fits into the case, take care not to damage the board when doing this. Your print will need to be of a good standard.  The back plate then clips in place, don't forget to put the wires through the hole in the plate.

All items should print well in the STL's orientation.