Did my engine and battery covers recently.
Remove covers and scrub with hot water with a little bit of fairy liquid to remove any grease or oil then rinse and dry. I used those green scotch brite pads as they rough up (key) the surface at the same time.
Scrub again with anti-static wipe (panel wipe) to make sure there is nothing in the surface that will lift the paint.
Plastic primer, couple of "light" coates 15mins between each.
Leave about an hour to let the solvent come out.
Colour, 2-3 "light" coates 15mins between each.
Leave over night to harden.
Laquer, 3 "light" coates 15mins between each.
Ive only used light coates to avoid runs and to minimize the risk of the paint cracking over time.
I used halfords aerosols 300ml, 1 of each, primer, colour, laquer.
They look really good i think and cost me £17
Hope this helps
Dan