your right I looked at your diagram incorrectly.you are putting the major tube on top,why not do it like the mystere and put it in front of the forebeam just inside the hull and in back of the rear beam again just inside the hull. these beams are then throughbolted together. The smaller support struts are then angled inward and attached with the (outside) beam to hull bolts.The seat actually should not sit as parallel as the deck but slightly angled upward (5degrees).The same tang as the hobie 18 can be used to attach the smaller strut.Remember to cut an angle in the pipe of the smaller strut so it sits flush on top of the tang when the wings are deployed.The wings are the best for cruising and short course sailing but they are back breakers in the ocean in some distance racing.