OK, I'm in a similiar situtation, just with a house.
Tell roommates. If you can't trust them to know you have a gun, you probably shouldn't have made teh decision to live with them.
Get a small safe. Even if you trust your roommates, there is no reason to trust their friends.
Make sure your roommates know what to do should they come across the gun. I don't like advertising, but I got a sign in my room advising that any guns may be loaded and to not touch, and a note in my drawer I keep my CCW advising not to pull the trigger
Oh, and all guns not under my immediate sober control are locked up before any drinking. End of story.