It might have been possible to slide it between the frontside and backside, but it frankly never crossed my mind to try—that would have been a pain to wrassle with every time I needed to refill it (also, I had to have a piece of high-density foam between front and back, because the seat fabric stretched enough that my vertebrae were resting directly on the buckles, which got to be a real problem). I had the unbottle slung on the outside. A couple straps of 1" webbing ran around the seat to hold it. I never noticed the straps when I was in the seat.