I have no experience with Tyvek as a cover, but it is apparently used:

http://www.widgets.ws/prod/Barts-Wat...at-Covers.html

We use a hevay duty tarp on our boat. Some synthetic textile covered
with PVC on both sides. The kind you see on covered trucks. Definitely not
lightweight, but very durable. I have no idea of the cost, as it came
with the boat when we bought it secondhand.

--
Strange attractors stole my wife