Tuesday evening, I drove 280 miles home from NY, thru a snowstorm. The car (with new tires) did well, but when I the next day, I noticed that the undertray, beneath the drivers seat was hanging down and packed with snow/ice.
I melted the snow/ice and found that I was missing six of the fasteners, with no other apparent damage.
I guess snow started working it's way underneath and forced off the fasteners. Previous to this no fasteners were missing as I had just rotated the tires a week previous and been underneath.
I had a hard time finding these fasteners. Three of my local dealers didn't have any in stock.
A PA dealer near where I worked said he could have some the next day. These babies were $2.50 each.
A 15/16" socket removes/installs them. (or corresponding metric).