rust in the pinch welds around the bottom of the door

[Island Medic]

I am repairing the rust in the bottom of the door. I am not going to be using patch panels. I will be hand making the patches and welding them in. I was thinking of pouring some rust mort into the bottom of the door and allow it to go in the pitch welds to convert the rust that is there. I have been reading about the phosphoric acid. Sounds like it has to be rinsed out after the application. Has anyone done this, or should I just cut open the seam and clean it out mechanically?

[Ontcalimo]

The acid works well. I would then brush it with steel brush, rinse it out and dry it. I would also pour some POR 15 rust paint on it. I bought two doors, and I am planning on filling those areas with short stand fiberglass or por 15 epoxy putty so water does not sip through there and only exit through drain holes. I hope the proactive measure work in long run.