I have been using the Kifaru Doobie Express as an underquilt with a Claytor hammock turned upside down.
I've been using it indoors so I have not really tested it outside in the cold but it is like it was meant to go together.
The Doobie Express is a Climashield over-gear poncho with velcro on the sides. Opened up, it can be used as an overquilt but it's dimensions are fit the Claytor hammock perfectly to be used as an underquilt that you put between the hammock and the bug net with the whole hammock used upside down. All I did was stick on matching strip of velcro to the hammock that can be used with the ones already on the Doobie Express. The bug net then keep the thing tight to the bottom of the hammock without compressing it too much.
On the plus side, you can also use the Doobie Express for it's original intended purpose and thus save on weight/extra gear - as a warm up layer in camp when you stop moving. I figure it should work at least down to freezing and it's "free gear" because you can use it in camp anyway when you are not sleeping.
I'll let pics describe the rest.
How you wear it.
Added velcro to the bug net.
Use it upside down.
I have also used plain ol' rectangular 40 deg sleeping bags opened up in this manner and have been out down to 15F with no problems - no shifting of the bag because the bug net holds it in place nicely.