I've gotten it fairly easily every day with 2 characters I'm taking through banner. Just have to wait out the rockets. Once the explosions stop, I start getting a little more brave. Fact is, rockets will rip you up in no time, and they should. Rockets have a blast radius, and blow things up. A thorn or last word user will rarely out gun me when I'm on a chain gun. I actually try to find stragglers when I'm going for machine lord. No matter what, a 2 or 3 on 1 fight usually results in the solo guy losing, no matter the weapons being used. Why rush a crowd that will mow you down in seconds? Try using a funnel effect, like fish in a barrel, or don't visit the high traffic spots at the time. Pick of the guys trying to flank. That's what I do. Even rocket guys get mowed down sometimes, if they get a little wreckless.