In order to get good welds, you'll need to clean the paint off in the immediate area. I would use MIG and weld the entire length of the crack using weld dots. I'm afraid you're going to lose some paint. If you just put a tack at each end, it won't stop the crack. Here's a couple of photos of the repair I did on one of my fenders that had similar but worse damage.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
