I can't understand this fixation on bondo, which is a moisture absorbent polyester filler, by those who do such good work and then want to use a cheap arse rubbish polyester filler. Crying out loud, go marine, use a epoxy based filler with glass balloons which is light and moisture proof and which you can fill with integrity as deep as you like.
Thats my little rant, once and for all, do it right and get over this bondo fixation. Body shops use it because insurance companys won't pay for quality.