A lot of your paint stores will sell a product called "Prep and Prime" or something of that nature. What it does is prepare the metal for primer, but at the same time it primes the metal so that it will not rust. It also cleans the metal and will get rid of light rust. I think last i looked it was about 18 dollars a gallon but it makes the metal ready to paint and you can leave it sitting for a long time without having to worry about rust. You can also weld on this.