I agree with all the answers from everybody. We never have bondo greater than 1/8" thick, it will crack. Preferably you want the filler as thin as possible. You need to spend more time straightening the metal, pick and file, hammer and dolly, heat shrinking etc. This takes a lot of time, that production body shops won't take that amount of time because it cuts into their profit margin. As a hobbyist with body work experience we can take as long as it takes to get the panels straight. Then a minimum skim coat of filler and the proper block sanding technique will assure that everything is straight. I am partial to Evercoat brand "Z-Grip" or "Rage" fillers. They sand easy, have no pin holes ( provided you mix the filler and hardener correctly) and don't shrink or stain thru the primer and finish base coat/clear coat paint.
