You were supposed to put the metal joiner through, then glue and insert the covered horizontal stab. After the glue has dried, put the hinges in and glue the elevators. When you put the last elevator on just make sure the joiner is in the slot. Later on I put some epoxy into the slot to make it stiffer. At the point where you are now I would probably just make a slot and put the joiner through it. A wooden rod might not hold up. Good luck.