I've had good luck with POR15 in the past.I. have the internal frame coating, going try it out inside the frame rails. It can be messy from what I heard and read.Not apples to apples but on my bronco I’m using Eastwood platinum as a base coat then coating it with Eastwood chassis paint. Also using their internal frame coating for the boxed sections.
I personally don’t like por15. Onechip in it and it’ll start flaking off.