You need something like polycarbonate or PETG. Both are impact resistant and can easily be cut , shaped, drilled etc.. Acrylic although you can drill it will crack from a stone impact. You can actually get a nice textured sheet in black, 2 or 3mm should do nicely.. You can hit both with a hammer at it will just bounce off it!
Normally come in a 8" x 4" sheet, try a local plastic company. You should just be able to roll it up to fit it in your car.
Steve