We do a LOT of custom mailboxes for a local community. The plain black boxes have to be repainted in their colors. The clincher is it HAS to be a specific paint and it's latex only. Does anyone have any tips or tricks on what the best prep, primers and are for a durable finish. I typically rough the box up with some sandpaper or a scotchbrite pad, but good adhesion seems to be hit or miss. So I am open to new ideas.