Resurrecting this again. Doing this the simple way:
- Tree shaped 1/4" shank rotary file for my grinder
- JB PlasticWeld, which according to every review I've read is amazing
- Motospray Plastic Fill
- 0.6mm aluminium sheet
Already own: rivet gun, blind rivets
Process
- drill out ends of cracks
- Rough up bumper front and back
- Grind V-grooves along cracks
- Thoroughly clean and prepwash the bumper
- Resin to close cracks up
- Back areas where plastic is entirely missing with aluminium sheet. Bond + rivet
- Plastic filler over holes
- Contour everything and add filler over repairs as necessary
- Plasti-prime
- Paint
I mulled using a fibre-backed bridging compound, but decided the holes were small enough that it wouldn't be necessary.