OK, i do this for a living!
If you sandblasted it and let's say you intend to do somemore work in a day or to, use the metal prep, put it on good and wet and leave it alone, by this I mean don't put your hands on it at all, it will protect it for a few days from the air, that is if it's in or under some kinda structure, some of these type products won't allow Epoxy to adhere to them so you need to know what products do what, if you can't afford to by the good stuff, you will get what you pay for! sorry for that last comment but it's the truth, many people have come into my shop with these spray can products on their ride, this stuff will almost always cause more problems then they fix!
You can go to any PPG store and buy Black or grey Epoxy (never white,no rust inhibitors) with the hardner for 60-70 bucks, this with some reducer is enough to do quite abit of work, just remember, epoxies are sealer type products, just cover the metal don't try to FILL it! Epoxies won't last for ever so get some two part primer/2K (not Laquar) on it as soon as possible!
