I used to scour building sites for Tyvek scraps (not so many of those any more, certainly not around here). But I have eschewed ground sheets of any kind for the past few years and my tents have not shown any more wear than they used to. In fact, Tarptent's website doesn't even recommend using them (but says if you feel you must, Tyvek is a good solution). My current tent, a Tarptent Contrail, has 6000 hiking miles and one Northern Tier ride on it, as well as numerous overnighters (hundreds of nights total), has never been pitched on a ground sheet, and the floor actually shows less wear than the rest of the tent.