Okay, here's the scoop. I shave the side trim on my Honda CRX and had to fix a couple rust holes. IT KEEPS CRACKING!!! The car has not moved yet, it still has an engine swap going on. I've heard that if you build up too much body filler at one time, it cracks. I learned my lesson and now only apply in thin layers. How do I fix the cracks now? Do I just grind a 1/2" trench down the cracks down to the metal and slowly build up layers of body filler? Would that work?