One suggestion I can make is to beef up the cabin top where the door attaches. There is a lot of stress on those two ribs and they can break very easily on a hard landing. The wing tube slips into them, and the cabin roof covers them. There is an 8-32 bolt that secures the wing to the outer rib. If there is any stress on those parts when assembled, the shock of landing can cause the outer one to crack at the rear of the opening.