I love my Camelbak. I, too, do my really long rides on country roads with no hope of rehydrating, so I need lots of extra fluids on my bike- and it's the easiest way to carry them. I don't remember which model it is, but it's wonderful. Got the really expensive big one at a sporting goods store, then was in Bass Pro Shop (why? don't ask) and found another Camelbak for $13, so I picked it up, too. The night before a long ride, I'll fill the bladder half-full then put it in the freezer. In the morning, I top it off with water, and it stays cold all day. I, too, put water on my back and gatorade in my bottle cages. I don't mind it on my back at all, and I can carry extra goodies back there (but I run with my Camelbak on long runs, so something on my back doesn't bother me at all).

I would try it- it would surely work for you. And if you're not sure, buy (or borrow) a cheapie one to see if you like it.