I already killed Kreiger, so I think I'm close
Yeah that area where you died is the absolute last area, you're about 10 minutes away.
There is an easier way to do this area, btw, if you want. I'll put it in secret text so as not to spoil anything.
in the room before the crater with all the ammo and loot, start pushing the chair out of the room. Push the chair with you all the way to that huge double blast door that leads to the volcano. This can be annoying, because the physics on the chair are a bit off, but it'll work.
Push the chair underneath the blast door that's open. Throw the lever. The door you just came through will close, while the outer one that leads to the volcano will open. However, because of the chair, the inner door WILL NOT CLOSE all the way. So you can crawl underneath it, then just kill the rocket guys at will when they stand like lumps in front of the door.
Note, they can still shoot at you, so be careful, but this makes it a ton easier to complete. Once you've cleared the crater, there's just one more battle, and it can be tricky, but nothing too severe.