Here is how a fender seam isn't supposed to look. IT is all wavy and beaten thin after years of abuse. I had to build up the fender flip section with material and grind everything smooth.
Since the original metal is so thin and smooth, we made a piece of tin to used as a backer for the weld.
In this pic the fender flap has been built up and the tin piece is still on the fender. This gets ground off.