If it's just surface rust, sand it off and coat the bare metal with POR15. Level the surface out with a bit of fibreglass filler, and then prime and paint. It's a time consuming process...so take your time with it.
The POR15 is an important step. I've been using this product for a while now with good results. It's a rust preventative paint. It will stop rust from spreading or getting worse by isolating it from water and oxygen (needed for oxidation to occur). Normal paint does not offer this kind of protection. However, the product is not cheap, and it does have quite specific application instructions that need to be followed carefully. If you have any questions about the stuff, feel free to ask.
The POR15 is an important step. I've been using this product for a while now with good results. It's a rust preventative paint. It will stop rust from spreading or getting worse by isolating it from water and oxygen (needed for oxidation to occur). Normal paint does not offer this kind of protection. However, the product is not cheap, and it does have quite specific application instructions that need to be followed carefully. If you have any questions about the stuff, feel free to ask.