Body shop / paint guys will probably be appalled at me for saying this, but I would just sand it with some 120/220 grit paper to scuff it and remove any flaking rust and then spray that 2k primer right over any surface rust. Once you prime it, base coat it, and clear coat it nobody will ever know or care what the base metal looked like.
I've been doing this for about 14 years with Nason 2k primer filler and base/clear and have never had rust come back through. I even tested spraying just clearcoat over bare rust on a piece of metal. That piece of metal has been sitting outside in the weather for years and looks exactly the same as the day I sprayed it with no further rusting. The clearcoat sealed it and completely stopped the rust.