Dipping is expensive but the only way to go. Last car I had done was $6000.00 (for the three dips).
I collect Mopars which are also unibodies. First dip; the shell is dipped in acid that eats paint, seam sealer and rust and ect. Acid is neutralized and shell is returned to you. At this stage all the metal replacement is done. Second dip; it is dipped in acid again (to clean and protect the new metal that has been welded in). Third dip; the entire shell is zinc phosphated. The shell is then primed and the body filling starts.
The entire body in virtually rust proofed, there is no better process for preventing future corrosion problems. Since all the surfaces that you just can't get paint to will be protected. i.e. inner surfaces of frames rails, inner structures of hood, trunk lid, trunk pan extensions. Not to mention that all the rust on these surfaces (inner surfaces of frames rails, inner structures of hood, trunk lid, trunk pan extensions) is removed and neutralized which media blasting can't even touch.
The acid doesn't eat metal, so it doesn't weaken or lighten the shell. It only eats rust. Some cars are dipped and what comes back out of the tank is not enough to build the car back with. Car body goes in and a block of swiss cheese comes out. Not recommended for rusty bodies.
