Generally speaking, the sheet metal process is not the kind of pushing concave surface from the inside of the blade.

Instead, the exterior paint is polished off first, then welded to the concave part of the exterior with tools, and then pulled out, generally without touching the inside of the fender. If that happens, the rear fender or the roof is sunken, why not take the roof off and knock it? Hehe, so what you said is not feasible. If you really want to paint the inside, you can usually spray a layer of primer on the inside when painting.