Before each "wave" (as the first zeppelin is arriving, and then as the second and third are arriving), put 5-6 Return to Sender traps around the generator. These persist (at least until they collect enough bullets) and will collect incoming bullets for you. That leaves you free to work on the zeppelins. I did that, took down the first zeppelin by myself (just run inside, sabotage the generator, and run back out). For the second and third, I called the Songbird on the left one (looking to the back of the ship) while I went into the right on my own. If there's a Patriot inside a zeppelin, just shock and run past it, sabotage, and run back out. By the time you get out of the third zeppelin, the Songbird should be ready for one last strike to clear out any remaining patriots. I failed over and over, did this, and beat it with a full 50-60% left