I've never built a Dynaflite Mustang of any size but I did build a Jemco FS Mustang 40 back around 83. I thought the wing seemed a little weak and flexed to much for my liking. I sheeted the top front half and the center section of the wing. I then used a spray foam to fill the pockets in front of the main spar. Once it's dry it's very light and makes the wing really strong. It's also easy to do. I didn't make any other mods and the plane gave my many hours of pleasure flying it.