A good way to do this is by running through the level (easier after you have already completed it) sucking up crates and Scoutbots (those little electrocuting robots), and then jumping in the water. When you respawn at your ship, your ammo for the Suck/Vortex Cannon will be full.
Take it bit by bit; take out all the areas in one section before moving on. Jump and strafe to avoid enemy fire.
- Ratchet & Clank: Up Your Arsenal (first appearance)