If you're going to use the polyurethane (which I'd recommend, we've used it in two robots past) make sure you get the hollow tube material, not the solid cylinder. The pipe material comes with metal barbs that can fasten two sides together, whereas the solid core material must be melted together. Just a suggestion.
Here's a link to a really good thread to peruse at your leisure. It basically discussed the merits of polyurethane tube belts.