This is the longest mission in the history of Fallout, mainly because it's easy to get you head blown off 400 times during this section.
Once you get to the vault, you need to kill Elijah to gain the trophy.
To get to the vault it's a pain in the backside. 1st Section
If you've been nice to Christine, you got down here using her voice and not having to synthesise the voice of Vera.
Once you take the lift down to the vault itself, the annoying security protocols kick in. Once you reach the walkway around the leadpioes with poison at the bottom of the chamber, keep an eye out for blue speakers. When you get to the second room (with a corner to your right that lets you sit there content, knowing your skull isn't going to fly in to the next room. Look back to where you just came from, abovr the room you just left is a blue speaker. Kill it. Off high to the right hand side is another. shoot that, it'll make the next run easier.
If you have you weapon ready, holster it, and run up the gangway. Eventually you'll spot a termnal up ahead. You'll have enough time to get there, this turns off the alarms and more importantly, your collar, skull is safe. 2nd Section
Most people use elaborate ways to take down the holograms, bit my method means you only have to take out one.
Veer off to the left and wait til the first terminal you see, can't be seen by the holograms. Access it and change the holograms patrol route. This send the closest one off down the corridor we just came from. The next one, sets a second off to the right hand side of the room, this may seem stupid but bare with.
Holster your weapon if you drew it for any reason and make a dash over to the right. Once all the way over, look back to the way we came (towards the centre of the room) and notice an emitter on a beam, shoot this and it takes away the hologram guarding the door.
Head down to the lowest room in this section and use the terminal to turn off the alarms (this does NOT turn off the speaker in one corner lf this room,so be careful) . Dash back to the left of the room (where we started) and wait for our friend to move back up the corridor, head down into the smog, head left along the beams to find a toolbox, infornt of this is a code, pick it up.
Return to the room on the far right, and yse the terminal that we used to turn the alarms off to turn the barrier off behind the door guard.
We don't need to kill him, wait til he comes across the the right hand platfomr and use the right hand patg behind him to creep through the door. 3rd section
Run to the terminal up ahead and turn the speakers off, we're now safe in this corridor. From here, we can reach the vault.
Once inside the vault, Make a save so you can come back for.
Pick up as many gold as you can carry, also dropping any unneccessary stuff you pick up during this DLC. Some people can carry upto 10gold bars, depending on strength stat and if you have the strong back perk. I made it out with 8.
Save again if you like then acrivate the terminal.
Convince him to come downstairs and then hide behind the right hand side of the vault door. As Elijah comes through, cut his path out off and get his attention to turn him hostile, then shoot at him to he's dead. Trophy unlocked when you start to escape the vault.