I cut out a panel to seal the air flow out of my radiator so that the hot air goes up out of the vent above the nose instead of out the bottom, disrupting the under-car flow. The plastic is what the circle track guys use, a high density polyethylene (HDPE). It is 1/8" thick and pretty tough but reasonably flexible. Cheap, too!
The strange brass-colored things are "cylindrical Clecos" which screw up to make a tight fit but still have a long reach. They will all be replaced with 3/16" Avex rivets.
Regards, Neil Tucson, AZ