Hmm.  Really good suggestions.<br/><br/>I'm leaning toward him treating his Ultramarine background more with fond memories and a bit of team loyalty... (he roots for them like a sports fanatic does his favorite team) but shamed by his exile from them (and frankly, deathly afraid of having them hunt him down), he conceals his actual Ultramarine origins carefully from any who might betray his secret.<br/><br/>Of course that does not mean he does not secretly desire the power that activating his marine upgrades would give him... and he'll always be on the look out for a way to do that safely... (and gain a superior suit of space marine armor!) but it'll be a goal that he'll approach carefully, as he doesn't want to be killed in the process.<br/><br/>Given the crew compliment of both ships, though, is there any reason he needs to be a stowaway?  Is it possible he managed to secure a legitimate job on one of them, (perhaps with a forged identity to keep the inquisition from finding him...)  It might be easier to have him be a trusted member of the ship's crew, who the other characters may have noticed during, say, the recent space battle, (or being recommended by a superior officer for promotion, say, if our resident Rogue Trader expresses a desire for a good bodyguard / gunner to serve him more personally?