Yay
Sorry. I was a body guy for awhile, its amazing to me what I found stripping down cars for bodywork and paint. Bodywork is done with hammer and dolly, not a can and a putty knife.
Impossible to say what's under there for metal work, but I'd be willing to bet there's at least a 1/4" of mud on there.
Bondo, the cheap kind, is made with talc. It absorbs water. Over time, the bondo absorbs moisture, swells, and cracks. Left alone long enough, it will even rust out the panel behind it. I always used "metal 2 metal" by evercoat if I needed to use filler. Its aluminum powder based, won't absorb water, can even be drilled and tapped according to evercoat (I would do something else before I did that though). It gets a bad name from people that are used to slinging bondo because its hard to mix (doesn't change colors) and is more difficult to sand because of its hardness. But you'd have to sling bondo to know the difference, so I usually ignore those folks. You shouldn't need to use so much its a problem anyway.
If the body line is seriously damaged under there, it may be easier to re-skin the door. But again, you'll have to strip all that bondo to see what's underneath. You could get lucky, I've stripped a few cars and wondered why there was so much bondo on them after I was done, they were much straighter than the pounds of bondo would lead you to believe.
