Mike,
I did a frame off resto on a truck a few years ago. Stripping the frame to bare metal and painting it took me all summer to do.
I used an assortment of tools to strip it. Needle scaler, grinders of various sizes with a couple hundred dollars of disks and such, torch and scrapers, and finally glass media blasted. Every nook and cranny was stripped to bare steel.
I then applied epoxy coating and Raptor bed liner over the epoxy base. Yes, the polyurethane bed liner is somewhat brittle and it can chip with a hard stone hit, but the chip does not go into the epoxy base. The barrier remains intact.
I have used POR 15 too. It is good paint, but it needs rust, or at least a rough surface for it to stick to. On smooth bare metal, it will easily peel away. Further, it is not uv resistant, so it needs a coating of something if exposed to sunlight.