I have to tell you, the best way to do that frame would be to epoxy prime it, then apply a urethane single stage paint right over it. This requires no sanding between the primer and the paint. It would give you a very durable finish, MUCH better than it had from the factory.
You can buy some "value line" epoxys and urethane single stage paints like OMNI, or NAPAs Martin Senour Cross/FIRE and have them do it. It is going to be MUCH better than Rustolinum, that is for wheel barrels.
Brian
