Sorry for the late reply. Seperating the outer cover is fairly easy. Stretch out the bellows to it's full length and leave it stretched overnight. Dampen the outer skin with a water wet cloth, don't soak it. Start on the bottom side with the seam. Just take your time and work it off with a putty knife to lift it off the ribs. With the cover off you can replace any ribs that need it with poster board and a light coating of white glue on the new rib, don't want it to soak thru the inner lining. When you replace the outer skin, start at the top panel, then the two side panel, the bottom seamed panel is last. If you make the seam run almost diagonal across the bottom it won't pile-up when folded. Spray-on adhesive works well for the outer skin. Leave excess at the ends and trim after gluing.
Take your time and good luck with it. No matter what, it WILL look better than duct tape;-)