Gunvalkyrie help needed!!! (possible spoiler, 3rd boss)

The four worms... I consider myself pretty good in the game overall, i've got cash left over after a fuel upgrade (80k) and a lockon upgrade (8k I think)... So I'm not a particularly bad player.

My problem is I've played the four worms probably six or seven times and I can never kill them. I can't even get to the halfway mark it seems. After I've done maybe a quarter damage, it becomes nearly impossible for me to shoot down those flying homing rock-things because a worm inevitable comes at me from behind with that invinci-shield thing goin on.

Am I missing some weakness, or is it really this hard? P.S. I have problems using the lockon while I'm in jetting around... is it even possible to use it efficiently while in air?

Thanks!!

I finally sat down for a few hours and just beat it.

But thanks anyway!! :)