trouble using bondo

you have to train your hand to tell you if its straight or not, there are small imperfections you just cannot see but you can feel. I like to use a fiberglass filler over weld areas (like everglass), then a nice polyester filler like Upol. trying to fix small spots at one time can be aggravating (to get straight), sometimes its much easier to cover the whole panel with filler and sand down, this seems like it would take longer but it really doesnt. this will also cover low and high spots you didn't see before.