[Fortuna solo bounty cave case drops]

I think the thing that makes this extra challenging is the fact that not only do a lot of enemies spawn, the cave has multiple very quickly up scaling floors but the enemies as I have noticed from the times that we've been unlucky enough to get THIS bounty. Spawn almost literally right on top of the cases a lot of the time. It's like oh hey, a case just spawned... with a guarding enemy squad of 5... 10.... oh good 15 and it's a rinse repeat of this every few seconds. I typically run in a group of 3-4 and we have a VERY hard time even managing to complete this... "Bounty" let alone even having a hope of getting the bonus. Explain if anyone can, how to safely keep the 4-7 cases safe from the spawn in defenders all at the same time? because we haven't figured it out and we've been trying.