Here's a proposal for the cult:
The Thousandfold Vigil says:
No one knows when the Death Cult first took root aboard the Scrap Hogg. It certainly predates its rusting hull plates and current occupation. There was no founding charter or no recorded martyr. Only the persistent fact that the ship has survived places and practices that should have damned it long ago suggest the God-Emperor's hand in its continued existence. And for over a millennium, the cult has acted as the vessel’s unseen immune system. As the Scrap Hogg works the worst margins of Imperial space stripping derelicts saturated with warp residue whilst crewed with the dregs of humanity sprinkled with some Xenos it is under constant exposure of the taint of heresy. Chaos rarely arrives openly. It creeps in through altered prayers, private symbols, and subtle deviations of faith. Sometimes the Xenos influence the crew to shift their beliefs. The cult watches for these signs with practiced precision. When corruption is confirmed it is removed quietly and completely. Bodies disappear. The crew quickly stops mentioning the names of those taken.
The ship's Xenos are tolerated by the cult out of necessity, not trust. The cult allows their presence so long as it remains strictly transactional. Any move on part of the crew toward xenos worship or ideological coexistence is met with swift culling. Betrayal is not feared... it is expected and prepared for. The cult does not challenge the captain’s authority or interfere with profit or navigation. It intervenes only when a line is crossed that others cannot see. Every captain learns the same truth eventually: they command the ship, but the cult is a power onto itself deeply interwoven in the bones of the ship. At times, the cult offers its services to bring the God-Emperor's benediction to the hulls that fall prey to the Scrap Hog. When it does its cultist sneak on board and silently remove anything that offends the God-Emperor of Mankind.
They call themselves the Thousandfold Vigil. The crew calls them the Quiet Ones.