Bikeless,
I admire your getting out and riding despite the ilieostomy, which I'm sure presents issues, especially on longer outings. My husband has a high colostomy which has caused innumerable embarrassing incidents and always requires back-up plans. You might contact your medical supplier and see what they suggest. Perhaps there is a bag that's been found by other athletes to work better. Perhaps somthing larger, or perhaps wearing a belt to hold it in place. Even some of that tape that's easy on the skin might give some extra reinforcement. There might even be some special solution you can use for longer rides that puts up with sweat and friction. I hope this helps a little, and Good luck to you!