As long as you don't use nylon webbing, you shouldn't get too much stretch. I usually use a drop bag, or my Canyon cooler has a big enough lip to hang from the frame cross bars. This season I'll go back to the drop bag. The trick with the drop bag is to make sure it's big enough so that you cooler sits flat in the bottom of it. I had a smaller drop bag that was a smidgen small for the cooler, and it rotated in the bag too much. Someone suggested a piece of yoga mat in the bottom of the drop bag, and that helps keep it from moving.
"We are all visitors to this time, this place. We are just passing through. Our purpose here is to observe, to learn, to grow, to love....and then we return home."
Australian Aboriginal Proverb