I failed a couple of times, but it wasn't THAT hard. You just have to clear the path much before the zeppelin arrives, and use the area explosion on those large groups of towers as often as possible, and don't forget to summon the wyvern. When they start yelling that they're not going to make it, save the game (if the Zeppelin isn't near-dead, of course). It doesn't take much longer in that part, but it's exactly when the zeppelin can end up blowing up in a few seconds if you're not careful.
