the grilles i just did with normal gloss black as many others (no lacquer though)
for the bump strips I used grey halfords plastic primer, cant remember if I did one or 2 coats. Did 2 coats of panther black from halfords. sanded with a 1000 grit sandpaper between each coat. then 2 layers of clear lacquer. finish isnt perfect but its ok from a distance.
I did mine before I put them on the car though cause I bought new ones (i had different bumpstrips before, not the ST shape ones)
My door handles are original from an ST, but you should be able to do them the same way i guess.
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2015 Chevrolet Camaro ZL1