Well I think I can understand where your concerns are coming from. I think though, that you are worrying that it will turn out bad, which is probably not the case. I can completely understand that you feel giving advanced warning to someone you are going to be in close proximity to for an extended period of time will prevent an awkward moment from happening if/when something causes your ostomy to be "discovered", like a leak, noises, seeing your supplies or whatever. I can also see you feeling like if you single out just the friend or friends that you are going on the trip with that they will in turn tell the others who will be confused why you trusted one but not all. The part I don't think will happen is by telling them now that they will feel like you didn't trust them. To me it is like sharing info about a case of diarrhea, need to know basis only, but this might be one of those times.
You said that you all go out a few times a week so I would guess that during these times the conversation does open up to some more personal conversations, i.e. relationship details and such. As far as the conversation starter, it seems you have already opened that door by telling them about your stomach surgery so all you would have to do is elaborate on that. Like others have mentioned, if you are worried about their confusion of why you didn't tell them earlier or why you are telling them now, explain that you needed time to adjust before you could bring it to them and with all of the group functions you are planning on doing together you thought it best that they know to prevent an awkward situation, i.e. someone walking in at the wrong time or whatnot. You will know when the timing is right when you are all together so I wouldn't push it none. Just wait until you feel they are in a state where they can understand the information. Just my take on it, hope it helps.
Total Colectomy with End Ileostomy May 27th, 2008
I was the Receptionist at a 2,000 member church during the years that I was sick and when I had my surgery, so EVERYONE knew about my ostomy, since I was on the prayer chain. People were very supportive and happy that I was doing so well after surgery, since they had seen me so sick before.
Now, I'm at a new job (at a church again), and nobody knows about my ostomy. I have told them that I used to be very sick with Crohn's, that I had surgery, and now I'm not sick anymore. Nobody has asked any questions, so I left it at that. I'm sure the time will come when I will tell someone, but it just hasn't happened yet. I'm not embarrassed by it, I just don't see the point in talking poo with people so soon after meeting them! :)
If you're not ready to tell people, then don't. I've spent many weekends at my sister's house, and her children don't know about my ostomy. It's possible to keep it to yourself, since you go to the bathroom alone. You'll know when the time is right and who you feel comfortable telling, especially after a pitcher of beer!
Have fun at the water park! I'm going to one on Saturday! woo hoo!!