Well you got to get the rust gone. If its surface rust sand it till its all gone then treat it with something like navel jelly to get rid of any you didnt see. Then get a self etching primer and treat the metal. Follow all directions on cleaning the surfaces. Once the primer is dry you could coat with any paint or rubber coating. You just got to get all rust 1st. Leave any or try to coat over it and you will have a night mare on your hands in a short time.
Got any pics of the rusted area?