What about Tyvek?
I always layer when touring. I bring a cotton t-shirt for comfort, 2 long-sleeve poly-pro shirts for warmth - one ultralightweight, one medium weight - I wear them riding as well as around camp (even in the rain - polypro doesn't absorb water), one long-sleeve jersey for riding on cold days, a fleece vest (those sleeves are heavy
), an ultralight high-vis windbreaker, and my rain jacket. When it gets cold I put all of those things on. If that's not enough, I go huddle in my sleeping bag.
I don't use a groundcloth under my tent. I've never seen the need, and it's one less thing to carry. It has never caused me any discomfort or inconvenience. I'm careful about what I spread my tent out on. But that's just me.