I have a friend who bought a 69 Camaro that had undergone a convertible conversion. The car had a bunch of strengthening work done underneath, but eventually (after some hard use) it started sagging, pretty soon the doors were rubbing, then they started opening harder (sticking). He blamed it on the fact that he beat on the car too much, but I am convinced that even with the most gentle handling, a car like this is doomed to sag, yeah you can go easy on it when driving, but gravity and turning in and out of driveways (where one front corner of the car always goes in higher than the other) are ever present demons, looking to wreck your ride. I do realize that you would be better off with a full frame car like the Chevelle instead of the Camaro, but like I said, this car had a lot of good (expensive looking) fabrication done underneath, and still went to hell.