This is another level that is much easier once you know the right strategy to use. Camping is a good way to get platinum here.

There is an alcove type area with a rocket launcher pickup in the back against the wall (it's a darker room on the second floor). Go back there and get the launcher.

Now move out a little bit and aim toward the ramp ahead of you that leads up to the floor you are on. Most of the time, the enemies will try to get to you this way so just shoot a rocket when you see them. I tend to aim at a spot right where there upper body will be when they get up the ramp.

You'll probably run out of rockets before it respawns, and if you do you'll probably die. One method to counter this from happening is to get the rocket launcher out on one of the connecting bridges before getting to the camp location. This will give you twice as many rockets to use at first, and by the time you run out, the rocket launcher at the camp spot should be back. It may take a few tries to get accustomed to it, so good luck.