rubbing samples on concrete. I tested a three ply, the codura faced one and the two ply.
The real difference between two and three ply weatherproof materials is the need to add a lining. In the two ply the rubbery weatherproofing is exposed on the inside, which isn't a good idea as it can get scratched and whatnot -- but if you are planning on using a lining anyway, as I am, then its fine, and about $5 a yard cheaper.
Anyhow, they all performed admirably, so should you be in the market, I can recommend any of these. Now I just (hah, "just") need to do my final muslin to get full yardage and I'm ready! My arbitrarily chosen 15 seconds ago goal is to have it done by the 1st of November.