I scuff the tanks, sides and flanges with red scotchbrite pad, prime with rustoleum metal etching primer, then paint with rustoleum semi-gloss black paint. This combo has held up nicely for 3 years. If I should get a chip in the paint, Ace Hardware will never run out of rattle can Rustoleum. I leave the coils/fins unpainted. They don't paint high efficiency a/c coils with black paint, and Ace Hardware appears to be out of dark matter black paint.
