installing screen under Duster's air vent
I did something similar to my Chrysler. Used black aluminum window screen and liquid nails or something like that. It's been under there for 7 or 8 years with no problems.
It is easier to do on a C-body because that whole panel is removable.
On the other hand, I saw a guy with a Mustang who had a piece of plexiglass with a couple of magnets glued on, that he used to cover the vent when parking outside.