[aerohead]

In the past, BIG LOTS, Wal Mart, and auto parts stores sold a lightweight polyurethane rubber floor mat system, which ganged together on the edges like puzzle pieces.
It's closed-cell foam, and could be tailored, and bonded with contact adhesive, to create complex shapes.
It wouldn't take on water, get heavy, and potentially fall of the car in a rain.
Velcro could be bonded to it.
I use it around the wheel arches and let the tires ablate it to it's closest fit tolerance.
Five, two-foot by two-foot sections used to cost fifteen dollars.
One side is embossed, kind of like star-plate aluminum, the flip side is smooth