About 10 years ago my wife made eight assorted size wing bags for me out of old sleeping bags (our camping days were over) and old quilts. They have worked well and are still in service today. Some are sewn on three sides and the wing slides in like a small sleeping bag, some open flat and are held closed by velcro, and some are two separate bags that slide on to each wing half allowing a fixed landing gear to hang out near the center. Different sizes and styles make them useful on many different planes. Total cost to build.....ZERO!