I have usually just used plastic sheeting like in drop cloths you can by from Lowe's or Home Depot and just cut to size, usually about an inch or two smaller than the actual footprint of the tent. Pretty durable and much less expensive, rolls down pretty compact. I've never actually had to replace one but never used it for the distance either. Not sure about the weight as I don't actually have a scale, but I would think lighter than Tyvek or the one designed by the manufacturer. You can usually find it in smaller sizes than this link if you go to the actual store. Could even cut out a couple and mail yourself a replacement in a resupply box along the way. Would be easy to replace at any local hardware store also.
http://www.lowes.com/ProductDisplay?...1#BVRRWidgetID