Taylor - You can power sand, but don't use a rotary sander. Use either a belt or an orbital sander. Bob is saying that the primer is vital for any paint. What I would recommend for priming bare metal is an epoxy primer. You do have to get rid of all rust to use it, though. If you are removing the iron and have access to a blaster it is an easy job. There are some products available for painting over rust, but they aren't cheap. We are using the POR-15 products for the high rust areas, go to
www.por15.com . Also there are the Corroless products, which are easier to use.
www.eastwoodco.com sells them.