Verado Lower HD unit.. painting
 

Best possible way to paint a HD lower that will last?

I did a ton lower units and sterndrives, and found that dry sanding bare aluminium with P180 , then Use a etching primer / washprimer in a few thin layers, then a few coats epoxy type coating , that is to dry sanding. P 240 when fully cured, and finished with urethane DD coat (. Desmodur/ desmoven ) Some say etching primers are hygroscopic, and that is right, but this stuff bites like crazy in bare Ali .

I blast mine Clean to Bare Alum , Re-Chromate them , ( I buy my Chromate from Aircraft Spruce in Georgia ) then black epoxy primer . Then PPG Concept 9300 or PPG DELFLEET 9300 Black , Single Stage
Put it on thin , Build it up Thick . Give it PLENTY of Flash Time Between Coats. It will Last as long as the Merc Stuff.