It took me all Saturday night but i did it after many tries with 3 guys in combat armour and 4 guys in heavy armour. for outside 2 Steyer Augs, 1 SLAW and 4 rotary grenade launchers. Killed the guys waiting outside the wall then waited for a couple to come through the gate, each one i had all 4 rotary launchers give him 4 rounds each. Then after a couple on minutes of none peeking out i took the wall down with grenade launchers right to left and giving each alien revealed 4 rounds from each of the launchers. Inside i switched to 3 CAWS and 4 MP7 and had no trouble getting the files.