Thread: venting blank panels?
Buy some inexpensive aluminum blank panels. Drill some holes in them. Rough up whichever side you want to be face-down with course sandpaper, then superglue some wire mesh (like screendoor material) to the bottom. Leave enough space so you don't interfere with mounting the panels to rails.
Now you have the airflow you want and a barrier to stop any loose items (like screws) from falling into the drilled holes.
Also, these two premade panels aren't that expensive:
https://www.modulargrid.net/e/steady-state-fate-ssf-8hp-vented-blank
https://www.modulargrid.net/e/endorphin-es-42-blind-panel-cable-holder