Will you be removing the coatings that is on there now or keeping it? The BEST WAY would be to remove the coating that is on there now so that the RustSeal can bite into the metal.
You can find complete instructions for RustSeal here: http://www.kbs-coatings.com/RustSeal-Information-and-Instructions_ep_38-1.html
You can also find Instructional Videos here: http://www.kbs-coatings.com/KBS-Videos_ep_90-1.html
For your application, you will want to apply 3 coats of RustSeal.
Please let us know if you have any additional questions.