x2 on the backpack getting sweaty. It will work, but it won't be that comfortable. I would look into putting a cargo rack on the back. They shouldn't be too expensive. Then, you can tie stuff to it, use bungie cords, get a milk crate or other sturdy box, and just stuff your things in there. It will also make your bike a lot more versatile if you ever want to bring home groceries or whatever.