ok...first of all dont use bondo or poly flex. those are not to fill in holes or cracks they are for slight dents and give you your shape before primer. for cracks go to an automotive paint store and the item you'll need is "fusor" its lit fusor 114 or something like that, or what ever one is for bonding plastics, it is a two component product that you put on the front with a mesh on the backside and spread it on just like bondo and sand it down when dry flip it over and do the same minus the mesh...
but the products to fix bumpers are normally too expensive for someone who isnt doing it every day you'd be looking at like 50 - 60 just for that one product. and then you have to repaint and blend out that panel.
it would be almost easier to get a new bumper or cover it with a lip or something
:twocents: