"... Pressure wash gently prior to painting.", is what bothers me.
If pressure washing with any reasonable force blows the paint off, I would question the primer adhesion to the frame. You can check it by sanding down to metal to test it. If the primer appears to flake off the metal when sanded/feathered down thin, I'd take a closer look at much of the old primer work. The blasting should have provided a good surface to paint over so it shouldn't be a problem, but strange things have happened.
POR15 is very durable and even likes a little rust, but requires a top coat if exposed to UV. The instructions are pretty clear on that.
