I run a lot of trails. I was never able to get comfortable with either the camelbak or the belts. In the end I've settled for hand helds (one or two depending on the distance). Some will complain about sore elbows/tendinitis...but most trail runners don't lift weights and have weak arms. I've never had a problem. YMMV
"And if a frog had wings it wouldn't bump his ass a hoppin'!"
- The wisdom of Nathan Arizona