If you have the pattern, with the midsection larger than either end, sew it up. Dampen, like casing, and stuff with flax seed, tamping as you fill. The normal crupper stuffer has a funnel and a steel tamper rod of small diameter, 1/4" or so. Add some seed, tamp hard, more seed, til filled. IF you don't have a crupper stretching/drying form, put a nail in a board. Put a small v-belt pulley over the nail and stretch the crupper, smooth side in, sewn side out, and pull....... nail both ends at once, or nail one, stretch and nail the second close to the first. Make sure the lengths of the tails are close to the same. Let dry overnight and then stitch the buckles and pieces together....that should take care of your wrinkles.