I replaced my tailgate because of a rust hole by the handle recently and the shedder on the old door was full of tears caused by previous repairs.
I had some heavy duty polythene-the stuff the builders use before laying concrete floors- and cut a piece off that to suit.
I then bought a tube of Sikaflex polyurethane adhesive, ran a bead around the door and stuck it on. The adhesive sets "rubbery" and can be peeled off with care, just like the original stuff.
Before they used the foam type material, all the shedders were polythene.