I used to use a product called rust mort that neutralized the rust and had a black coating were the rust was ,I think it is similar to a US product Ospo after that I would use a rust paint like rust oleum .I would also put some fluid film in there to keep everything sealed although I think it is not recommended to paint over the rust when you use fluid film or wool wax but I like the idea of treating the rust and I like the way fluid film works to keep the metal coated
