Story Related and Unmissable
When you start this part of the DLC you can earn a new perk by collecting all ten Intel Suitcases. See here for their locations: Intel suitcase - The Vault, the Fallout wiki - Fallout: New Vegas and more (credit to the Fallout Wiki for the link).
After receiving your new gear equip it and make your way through the various tunnels and caves, killing every enemy you see until you meet up again with Benjamin, in a cave further in. After you've regrouped you can take a back seat and let Benjamin do all the work as he can't be killed, just rendered unconscious. Whilst making your way through this next area you will encounter several snipers, soldiers and a couple of heavily defended bunkers.
The three guns to be destroyed are are in close proximity to each other and lightly guarded. Before you can destroy a gun you must wipe out all the soldiers who are guarding it, then you can plant your charge and get out before it blows. After the last gun has been destroyed the screen will fade out and you will end up in front of a General Chase, who will congratulate you.
WARNING: There is a nasty but rare glitch with the third gun when it blows up that can cause your console to hard-freeze. To avoid this glitch, save before planting the charge and don't stray too far beyond the safe zone.
The trophy will pop once the conversation with General Chase is finished.