Does he have any close friends, or is he introverted to the point where he has none at this point? If he has some close friends, it means that he probably has opened up to them about his issues, or even if he has a few friends at school he hangs out with. Maybe his parents are the same way (which seems likely from this camping trip). I think maybe one day you should just pick him up and take him out to a ballgame or something with you (or whatever interests him: video games, history, museums, space, etc), and see if he opens up talking about a subject he loves.

Just speaking personally, I'm a pretty quiet dude as well, and some people take it like I don't want to talk to them which is of course not true. For a while when I was growing up, I was one of those guys who couldn't talk about just any subject because I had no experience in those areas (at this point I can). But when I go to a Warriors/49ers/Giants game, I can talk the entire game about situations, players etc. Hopefully you can do the same with him in an area that interests him?