I recently started using oxygen for exercise. My oxygen supplier gave me a cloth "over-the-shoulder" bag to hold a D tank, but the D tank is fairly heavy, and not practical for exercising (unless I'm on the treadmill or stationary bike.) They also provided me with a cloth backpack that holds one C tank or M9 tank. At my flow rate, these last about 45 - 60 minutes if I am walking outdoors, but I need a better backpack. Any suggestions re good backpacks that will hold one (or two) C or M9 tanks?