I remember "water on your back with a tube" schemes for runners back in the late 1970s, though it's true I never tried them or a Camelbak.
Sure, whatever works for you! Just don't think that it's "seven or eight pounds." It's a seven-or-eight-pound weight that you are doing one-inch reps with, up, down, and sideways, sixty cycles per minute, for ten hours.
I'm lazy and prefer to push that weight forward as efficiently as possible. I keep my water in bottles, in my panniers, with one out for drinking. Bet my water stays warmer insulated that way than yours does on your back!
As with all thing bike touring, I will be the first to concede that it's all about enjoying the experience and little to do with achieving efficiencies. So I'm glad if people enjoy touring with Camelbaks on.