I use an etching primer when I know it will set and have to do work later. Cheaper and seals the metal. Then when all body work it done, a good sanding and sealing primer, followed by a base coat and top coat. Since most sealing primers have a time limit to when you need to apply the base coat. The etching primers don't need to be applied that heavy and leaves you with less sanding to keep the crisp lines. IMO
