I would advise against treads for these reasons:
Tread gets expensive. If you buy plastic tread, it's most likely coming from the UK (long shipping time), and isn't that durable. If you make tread (see this article:
http://blog.makezine.com/2010/10/27/...s-from-roller/) it can be very time consuming and heavy. If you use a conveyer belt type material, it's easy for it to slip and come off the rollers. I hope you take this into consideration, all the best,
-B