So here's two ends. Good thing you can't see the stitching (esp mom) or you'd be flabbergasted at it's ugliness.
The head end, with a hastily sewed "retaining loop" that only an acrobat can access to hook on to anything.
Luckily, it stays up totally fine by itself without the loop while you're in it. In a 55 degree bag (it's 47 degrees out right now) with no underquilt and just the tube on (in the bag regular, not like a peapod) I get a cold butt in about 3 minutes, so of course insulation is still needed... but, but... there is no major penalty in terms of heat loss when I WIGGLE! Seriously, I'm a wiggly sleeper, and your heat doesn't all just run away. It also humidifies the air a bit for you. Now, overnight, this might mean condensation, I have no idea yet, but I am pretty excited about this idea. In asymmetrical laying position, I can reach under the hammock and feel about an inch or less under my butt before the tunnel. So there's a nice gap, which I think will assist a short underquilt from wiggling and sagging. Also, it has a glorious tent/fort like feel and the walls are a little see through. All in all, neat! Cuts down on drafts in a big way too.
And as always, slides off for escape. The new head end makes it a little tougher to get under your butt when sliding, but still fine.