I carried one on the Long Trail although the shelters were so empty, and as it was my first long distance hike ever, I was often so tired I would just throw down in the shelter.
I went in August with a 45 degree down bag. I used my sleeping pad underneath me, it wasn’t cold in August. I HAVE slept in them at home (testing, testing) and had to bail out from chill after midnight, but not in August of '02.
The advice to try it out at home is wise, but you needn’t curl like a shrimp if you lie diagonally.
One night I set it up as a bivy, with the tarp off. The Perseid meteor shower (mid-August) was out and I wanted to sleep in the open, not under trees, to watch without the bugs. There are restrictions that require a hiker to camp at shelters above 2500 feet in some portions, if memory serves, so I just bounced my hammock ahead.
Only on one stealth site (??? near the end) were the trees not great for hanging; they were mostly dead. Nonetheless, I got the job done. It was tempting to string up across the Trail (and rising early), as those were the only live trees around, but the knowledge that moose use the trails for night travel discouraged me.
I could just picture the scene:
Moose: “Oooof! What the…!!!”
Me: “Ow! Hey! Put me down!”
Jan LiteShoe