Don't use fiberglass or bondo on your plastic bumpers unless you like wasting money. Fiberglass and bondo won't flex the way abs plastic does, therefore it will crack again if you use this method There is plastic filler for your gashes and there is something that basically welds your crack with plastic.The rear bumper can easyly be fixed wit Fiberglass! and alot of sanding and love..
Fotn bumper..Sand it down.fiberglass it or bondo...ur choice..and sand sand sand...prime - paint- clear- reclear-reclear- wait- buff-polish- done!!