Man, Ray was doing you a solid and you didn't even know it yet. That 1/8 inch rule is no joke either, because filler shrinks as it cures and the thicker it is the more it wants to move around under the paint. Add in a little heat from the sun or a door getting shut hard and that quarter panel was doomed from day one. I've seen guys pack filler in a dent you could hide a football in, then wonder why it looks like a topo map a year later. Once you start pulling with the stud welder you realize you spend less time sanding and way less product, so it pays for itself fast. The real move is getting the metal close first, then a thin skim to finish it, because filler is for smoothing not for building.