Space Hulk: Deathwing

This guide is for solo players who don't have online friends willing to spend 10 or more hours playing as an apothecary simply to keep you healed. Detailed here will be the method personally used to obtain it, but before reading further check out my guide on the Champion of the Lion trophy and decide your preferred approach.
Please note this trophy cannot be unlocked from normal play. Most players tend to be mission orientated and it would be very unlikely the required level 7 could be obtained before the mission objectives are met. Solo play or with a dedicated team is the best way to go.
This is not an easy trophy to get and may require multiple attempts to unlock it. To conquer it for each of the Space Marine Terminator classes with ranged weaponry some customization was required, namely Armour Boost/Bonus 20 and the Resilient perk. So concentrate all your accumulated points from multiplayer and the special missions toward buying these first, you'll likely need them to max out your abilities to Level 7 as required.
From the main menu select multiplayer, host your own game and turn off the Codex Rules. Select the librarian with your preferred choice of weaponry, then Chapter 1 and set the difficulty to easy. Once aboard the space hulk head down the stairs ahead and to the right of you, drop off the platform onto the corridor on the right and head straight down that corridor. Save your sprinting ability until the shooting starts, keep running until you make it to the doorway, pass through and then duck to either side of it. Keep it open, using the door frame for cover you'll be able to kill the genestealer hybrids with ranged weapons as they come to attack you. Beware of the hybrid Psykers whose attacks will deal considerable damage to your armour. Once the majority have been dispatched, purestrain, stalker and bio-blast genestealers will start to arrive, but by now level 1 should be nearly complete, when it is your health will be restored.
The corridor you're in should turn left direct after the door, then right, follow it until the second right and go through the door at the end. You'll enter a circular chamber with a large bell in the centre. Go through the first available door on the left out of that chamber, the one with the gun emplacement above it, close the door and seal it behind you. The corridor you are now in has steps descending down which gives you some height advantage other the encroaching swarms of genestealers. This is something you are going to need to prevent the irksome bio-blast variety from getting close and exploding against you. Simply remain in this corridor, retreating back when the hordes attack. When you hear the distinctive cry of the bio-blast genestealer, find and concentrate your firepower on it. As you unlock your psychic abilities use them, particularly on the larger groups or when the bio-blast are around, but try to hold off their usage until your bolter is running low on ammo.
Keep this up for just over an hour and the trophy will pop.
The trophies Killing Machine, Phoenix Light and Chapter Pillar were all obtained using the same approach as described here.