I needed something ASAP for a trip this weekend, so I snagged a Chinook 9.5x12 for my grizz bridge.
I'll snap some pics and post em up both of the tarp packed up and set up.
My testing with Tyvek did not give me warm fuzzies about its capabilities. It is MOSTLY waterproof, but does allow slow leaks. Also, based on other reviews it is prone to tearing along edges (tape edges and such).
Anyway, I hope this tarp works. If not, it'll be on the For sale board come Monday. LOL!