Marine rooms are basically just cells where they sleep when not doing marine stuff and they are usually away from the others as its their own personal room. You can claim the room if you wish its up to you. Remember your a night lord you dont need permission for anything.
I was thinking if Kesh can just commandeer Tal-Zahn's quarters?
Would these be shared with others e.g. like a dormitory? Or would he need a key + permission (etc) to access them (if so, who from)?
if it would make things easier, do you want my post to be "the thing which gets him promoted to First Claw" (ie so that it's kind of an introduction)?
I think I'll go with him having a boarding shield + plasma + chainfist because I think Box's character has a missile launcher(?)