Because I have a lack of equipment to fully stock my 19" server rack, and that metal cover plates are quite expensive, I decided to print my own.
I have made 3 models;
1; A 1U blank cover plate
2; A 1U cover plate with horizontal vent openings
3; A 1U cover plate with vertical vent openings
The parts are interchangable, in the photo I used the sides of the horizontal vent model with the middle of the blank model.
Rotate the parts on their front and use support for the side parts.
After printing, just remove the supports.
Then sand the flaps a little bit so there is a nice flat surface, and glue it together using CA glue (CyanoAcrylate).
Having an IKEA LackRack myself, and actual server cages at work. I jumped back and forth to design a model that would fit both of them.
I first took the measurements of actual 1U equipment and then adjusted the inside stabilizing fins so they would fit in both.