Just curious how the pros deal with lap seams such as where the inner fenders and braces meet the firewall. Even the "rust free" cars seem to have plenty of rust in these areas when the spot welds are drilled and the metal is peeled back. I can't imagine anyone goes through the trouble of deconstructing these areas to treat and weld back up. They would never look right.

If the metal looks good, I generally just coat with epoxy and use seam sealer in the appropriate areas. But that doesn't change the fact that there is unseen rust.