I also used hardware cloth but am using tension of the hardware cloth to keep in place. Cut the outer edges so the hardware cloth will 'bite' into the plastic. Also put a nylon tie on for extra support.
The body shop says this is diamond-grille cloth (1/8 x 1/4 more or less) for racing cars, for the same purpose: keep debris from passing, let air through.
To repeat, I met a MO owner who took a small stone in his A/C unit, and paid $600 to replace A/C (Canadian prices here). I paid the body shop $187. to remove bumper, glue and screw the grille cloth, and put it all back, so there are no "in progress pix".
In this pic, there is a sunrise effect that is only in the pic. You don't see that in the real world.