Waxed canvas/cotton need to be rewaxed after some time, whereas the thermoplastic polymer type dry bags are tougher layered and will be lower maintenance. Sure the liner keeps everything dry inside. The wax will also show scuffs a little easier. I personally use Green Guru pannier bags, which are made of recycled inner tubes and can handle heavy rain for 30 mins before the water will enter into cracks in the seams once saturation occurs. The backpack is very nice and convertible into a pannier bag.