The problem with bondo is that these auto parts places will stay open 7 days a week to sell the stuff, and people like to just blob it in there by the gallon and smooth it out and paint.
Personally, i'd rather have dents in my truck than have them filled with bondo.
I say smack the dent out as best you can.. then smooth it out with lead.. with alot of time, patience, and skill, you can get the dent worked out to where very little (if any) filler is required.
If you're not skilled in body repair.. find an old Pinto fender or something, and knock the hell out of it, then fix it. It's good practice.
Full on rot should be cut out and replaced with new metal (a patch) with filler used sparingly to help blend the patch in with the original metal.
