DONSZ: I try not to use filler at all. I prefer to metal finish if at all possible. First choice for filler if needed would be body solder. That would be for dents and such I cannot reach with a Stud Welder and/or a hammer and dolly. It's permenant and you will never have to address it again. If I have to use a spreadable filler, I use Duraglas by USC. It's reinforced with filberglass. It's waterproof, rustproof, and will not crack. For smaller problems, I use a Glaze Coat from Evercoat. Some guys like to just slap filler on everything. I like to take my time and do it right and never have to worry about it again.
