My preference is Kirker Epoxy. Cheaper than most epoxies, easy mixing (50/50), no induction time (just mix and spray, no wait), and it can be sanded fairly well. Most epoxies don't sand well. It sticks to metal like glue, well it is an expoxy, right.
Let it flash for 15-30 minutes and spray a sandable primer on rough sheetmetal, or right to your finish coat if the metal is smooth.