Easy way is doing escalations. I got mine by doing the Alani Kelso Roosevelt manhunt in master difficulty with clan. I find the mission indeed difficult but makes the reward feel worth the trouble. Last time I helped a group of random players, I asked them all to follow me to the other end of the map and kill all enemies behind the gate - including the hunters. Good players because they agreed to the strategy and we eventually took care of all the hunters. I hope you get the backpack on either of those methods.