In my opinion, the problem with welding any type of panel in general is that the inner surface of the panel is left vulnerable to rust unless it can be recoated. The extreme heat generated in the welding process will remove any protective sort of coating on the inside where the welding was done, so the inner side of the panel must be recoated or it will rust again in the future.
When replacing body panels, I have gone to using flush mount rivets and urethane adhesive/sealer whenever possible here in rust country Minnesota USA...