I need your help. I've decided to start my first DIY UQ. I'll be using a poncho liner for added comfort. I'll fold it in half lengthwise, sew it together and sew baffles in it to fill with down and then sew the baffles closed and add shock cord to attach it to my hammock. My question is, how much 800 fill down do I need? I'll be using it in the mountains of east Tennessee and I'd rather be warmer than chilled. Any help is appreciated.