Yes, those doors fit like crap, you have to do some mods to make them better. Yes the skin is spot welded to the bottoms of the gutters and then lipped over the front above the windshield and then in a pinch weld at the rear over the rear body panel. I believe to get to all of it as the factory did would require removing the inner panels. I chopped the top on one years ago so it's been a while but damn I can't see how you would remove the skin without removing the inners structure that is spot welded all the way around.
Why do you need a new skin? Can it be fixed?