The main reason Crobat isn't suited for battle versus Steel types is because of its typing. It learns mainly moves for Poison, Flying and status changers such as Confuse Ray or Toxic. I can suggest Hidden Power (Fire, Ground, Fighting for super effectiveness, or Electric, Water for normal) or Heat Wave for Steel's Fire weakness, but it would have to be covered up by stat loss by using something like Nasty Plot. Also viable would be having it learn Super Fang to cut the HP down somewhat effectively by halving it.