Most restoration experts well recommend spot welds were orignal and butt welds every were else. Take your time, practice on like metal before welding the the patch, utilize heat dams(wet towels) to reduce warping and were posible use a light source to eluminate any pin holes. The butt weld when done right well not allow mosture in from the back side as well the lap joint. even when seam sealed lap joints are suspect. just my opinion, good luck.
