I think I would go along with Whitey on this one if it is just a small spot. I’ve tried about every rust converter product out there though and don’t be surpised when the rust comes back. Two part epoxy primer seems to be the only stuff that slows it down. The best way would be to sand blast all of the rust out of there and then acid wash it, then prime and paint, but for just a small spot, go for it.