When I started restoring my 240Z, I checked the Net for new ideas and procedures. I noticed a large number of restorers were not using Weld Thur Primer when
when replacing new panels or repairing old ones. Weld thur primer is must on areas to be welded. It goes a long way to prevent future corrosion on that area.
This because the heat from welding eliminates any paint or regular primer that was there previously. Rust proofing the area helps a little but in most cases can get into those confined areas. So corrosion can occur in only months after welding. Check out-
So buy Weld Thur Primer (NAPA has it) and spray all sides of any weld( inside and outside) with it. It will give additional peace of mind.
welded area before
welded area primed