I don't worry so much about DS's roomies or even his floor mates when he was in a dorm, its the friends of friends etc. Its easy to walk out the door with an ipod, ipad, iphone, wallet etc. in someones packet, not so easy to walk out with a larger locked box, a footlocker etc.
A bit of caution goes a long way. I want my DS to learn to take care of his things, to be cautious and remember he is no longer in his room in our house but out in the bigger world and there are lots of dishonest people in the bigger world.