So I take Yazoo's advice and buy a Montbell UL SS bag from Modern Mountain Man, but there's one problem. They were sold out of the #2 so I had to get the #3, see? That won't be a biggie for me most of the time because I am a slouching, back-sliding, mouth-breathing fair weather hiker. But here's the deal, I'm hiking the High Sierra trail in late September and I'm thinking that a 30 degree bag ain't gonna be enough. I have looked at a silk liner (+10F) and the other day a guy told me that I could make a bivy out of two trash bags. I don't know what to do. Do you lightweight experts (I meant that in a good way) have any suggestions?