I just noticed that this post was for bivy hunting! Good luck if you are a die-hard bivy nut. I've tried it and it doesn't work for me! My preference is to pack in a small, portable camp that I hunt from each day. Obviously I'm not as mobile but hunting each day with 30 to 50 lbs on my back doesn't work...what-so-ever for me! Try quietly stalking and glassing with a 30 to 50 lb pack on your back for a couple hours and you'll see exactly what I'm talking about! Try it for a few days on 45 degree slopes with brush and rock....and it is craziness! Toss in rain, wind, and snow...oh my God! There are a few brutes out there that can effectively hunt this way but I have tried it on several occasions and failed miserably!