I just finished a 1/3 scale biplane. I attached the koverall with nitrate dope and followed it up with 3 more coats over the whole plane. After priming (no pinholes), I painted it a dark camo scheme. Everything looks great inside the shop. I went to the field today and put it in the sun to run the motor. Much to my dismay... the open bays sagged. I thought it was the dark paint job. I even cut a hole in one of the cockpit floors to let the heat escape.. As soon as I take it out of the sun.... everything tightens up again... What gives with this? I thought Koverall gets better and tighter with age? Please make sense of this for me