For steel frames there's a product called POR15 available on Amazon.com. A pint of that is more than enough. There are YouTube videos demonstrating its virtues. The frame has to be stripped of paint first and etched with phosphoric acid, aka "naval jelly". This stuff looks like it might be better than automotive two part epoxy but I haven't tried it.
Last edited by Clem von Jones; 10-17-19 at 11:20 AM.