Go with the GG med weight polycryon? stuff. Keep it out of the sun as much as you can, like pitch your shelter late in the day or in the shade. Tyvek is heavier than you think. I cut my GG groundcloth down to fit my floorless Tarptent Squall, it weights around 4 oz. The cut to fit Tyvek that Henry supplies weighs around 6 or 7 ozs. if I remember right, not at home now to reweigh it.