I redid the bottoms of my 4t6 doors by cutting and folding the exterior skin. Next i treated with a product called Right Stuff picked up at local FLAPS. The existing door was flanged and new skin was tacked on. A little filler, some primer, sanding, a little more filler, some more priming and eventually some paint. Maybe some ideas for you in pics below. Good luck and have fun.

Dan
http://rides.webshots.com/photo/1512695955071274430lWhMwv