Some of the things affected by  casual mode:  The zeppelin survives a lot longer, your creature is stronger, you receive less damage and the enemies are easier to defeat.   
Is there any chance you could make a wimp mode for this mission?  I would just like to get past it.
I have tried to complete it more than a dozen times, it doesn't matter how quickly I destroy the towers my zeppelin still crashes, it is so frustrating.