3m adhesive spray.......scuff the inside of the panel , and make sure you cut enough extra to get about 1" of material beyond the hole you are covering ( yes the vent goes inside the plastic). Spray adhesive and set mesh, use a plastic, dull paddy knife or wallpaper blade
Hot glue also works well
Squeeze glue onto plastic, then lay material. Use something flat , we use cardboard pieces, to press the material into the glue, bonding the two together