I'm thinking of running an Only War game, but due to lack of time am thinking of going with a published adventure -- of which there aren't many.
Going through the WH40KRP advantures that I DO have, I think that Shades on Twlight might be adaptable -- having grunts on it instead of Acolytes might give it kind of an Aliens feel. BUT I have problems rationalizing what the IG would be doing on a space hulk. Also, I would want to take out Brother what's his name.
Any ideas? Perhaps the group's IG troop carrier happens to emerge into realspace near the hulk and they decide to investigate. Or -- there are secret inquistorial orders to the regiment commander to investigate (a la Alien), What do you think?