You need to sand any painted areas to get the loose stuff off, and any gloss off of the paint. The herculiner will need some "tooth" to grab onto. Any rusted areas, use POR-15 on it. (POR=Paint Over Rust). It's a converter and sealer in one. Once that is dry, and all of the sanding debris is removed, rub everything down with lacqueer thinner to remove any oils from your skin that may have got on the surface. Work from the farthest corner out-of course. The first coat is just a base. The second coat is where the thickness and protection comes from. Once coat would be fine in your case, I would suspect. If you're not happy with it after you drive it for a day or so, go back over it. You can add to it much easier than you can remove it.