I’m restoring a 1950 Chevy pick-up truck, my first restoration project. I have finished patching the four fenders, and have had them media blasted(glass bead) they have been treated with a zinc-phosphate protective spray. I have some low areas (due to warping) where I welded patch panels. I have hammered them out as much as I dare. Additionally about 80% of a couple of the fenders are pitted. I watched Kevin’s z sled video, and another short video have shown a couple of techniques but I’m getting a little confused because I have a combination of issues to resolve. My question is…. What is the filler to start with? Should I cover the whole fender with it, or only the low areas then apply glazing putty over everything or even filler primer?