Thats what I currently too, and it works pretty well as long as you change it at least once a week. I would say the only disadvantage would be if you didn't have some kind of drainage set up for your water to go. Otherwise it gets wet and becomes quite a mess.
If I were you, I would use paper-towel at the bottom, because it absorbs more of the mess and excess water, and it doesn't mold or create a stench like newspaper. Just my opinion...