Whenever the frames on my cars have been exposed, I have spent extra time with the bondo, and a varying grades of sandpaper wrapped around a peice of heater hose---resulting in ultra smooth welds, and mega sore fingers.
I always have a quiet little laugh to myself when at car shows, people have came up to me and said "Gee, I sure wish I could lay a bead like that". ---little do they know---