you are a very sharp guy!!the front tube is for rotation of the wing only..not a spar.i put 3/8 ply inside of fuse just around the hole.then i cut and glue the front tube in the wing only.make it just long enough to go through the ply ring dubler.ther is about 1/2 inch clearance at the bottom ,lower corners ,of the tank. you can run fuel lines and wires in this area.. tank weight is 2.3 oz..