The best rust converter is called Vactan, it is the original chemical formulated by ICI and it can be sprayed or brushed , it is water based and cheap as chips on EBay, it can be primed and painted
if the corrosion after scraping & wirebrushing isn’t severe it can be painted with a paint called Fortress from B&Q, no primer is required this paint is manufactured by Tor Paints' if you buy from them you’ll save about 30%, unfortunately I can’t remember Tor’s name for the paint , it goes on quite thick and produces a stove enamel type finish - read the tin carefully before using
