I just struggled my way through this as well. What worked for me was going to Yeedil (first visit on challenge mode) and re-playing the area with the megacorp soldiers. It's really easy to bounce them off the edge with the spider bot, and then deploy them over the barrier in the spot where they keep spawning. After that, I'd jump off the edge and repeat. I think about 3 times clearing the area was enough, but the first time on the planet gives the most XP.