I have had the same problem with rear doors. The simple fix for dented doors is to cut the inside recessed area out with a grinder, carefully cutting a smaller opening than the recess. This way a piece of metal can be spot welded in place so that the cut-out piece fits in without falling out. You can either screw the panel in and cover it or spot weld it back in place. With the panel open, you can get to most spots with a dolly and hammer. I know there are other methods for doing this, welding pins and pulling them or using a puller. The problem with these methods for me is my exposed welding abilities. I am much better with body tools.
