I'd give the Tyvek a try. I normally sleep in a hammock if there are trees, or under a silnylon tarp if not, so ventilation is everything. If you have any ventilation at all you shouldn't have any condensation problems.
For lightness, you can also opt for coated nylon ripstop, say 1.9 oz.. It won't let anything through.
I DON'T like using plastic because it takes forever to dry when I pack up in the morning. A little gas permeability and everything is dry when I pack up.
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paul, texas KD5IVP