I have four different hammocks I've used...the double layered bottoms are best for keeping a sleeping pad in position, but there's more to that when using a hammock in cold weather (sub 40 degrees). I'm a hot sleeper, but you're going lose the light-weight advantage of the hammock if you want to sleep comfortably in cold weather. I usually pack my Swanndri wool shirt during cold weather trips, and this last spring, I actually slept on top of it for added insulation.
You're going to need some loft on the underside of the hammock...the pod is a method; I want to try a poncho liner as they pack down pretty small and I'm hoping will create enough loft to keep the underside insulated enough.
Here's what I'm going to try over the Christmas holidays (probably around 30 degree lows here in GA):
WarBonnet Blackbird
Snugpak Softi (can't remember the exact model, but it's a 40 degree bag)
Kifaru Woobie
Thermarest sleeping pad
Poncho Liner (the under quilt insulation)
Of course, I'm going to keep the fly tied down close and sealed as best as possible. I'll add my Swanndri shirt as extra padding/insulation and wear my cold weather sleep clothing (wool hoodie, silk-weight long johns, wools socks, glove liners and fleece watchcap).
To be honest, I think the separate hammock fly would make a good ground shelter cover. Use natural insulation for the ground along with your sleeping pad, bag and woobie or poncho liner. Even if you fire is far enough away to keep your synthetics from melting, a good reflector would greatly add to your comfort.
I'm torn, but I do want to try a cold weather hammock set up and see if the comfort rating will work for me. Just don't discount how cold that under draft can be in a hammock...even with insulation!
ROCK6