I am ordering some Miracle Paint this week and will let you know.

I have a half of battery tray that I would like to make complete, but the big issue is a big hole right by the corner of the rear window. I want to make my trunk watertight, and stop the rust

I think that I can brush some of the Miracle paint onto the backside accessed through the trunk. Now that I'm writing this that seems doubtful for the backside of the quarter panel

I am wondering about some spray on rust converter to use from the underside. I don't know which way to go, but for the outside it is definitely the Miracle Paint.

I don't know whether to get from this place on the net that sells a kit, or get it from this other guy for less money and get the stuff made for painted body parts. I guess I just answered my own question.