Kifaru Woobie Express hammock tube/bottom insulation
This seems to works very well and works with hammocks without a built in bug mesh, i.e. the ultralight hammocks, etc.
I don't think it would be a primary bottom insulation method but it works extremely well in a pinch.
You just form a tube with the Woobie Express by overlapping the bottoms. In use, you make the tube ends small enough so that it is over your shoulder (or knees) and then just gets held there by your shoulder with no gap under you. If you curl up, the Express alone can cover and cocoon your whole body. I use it with a zipped open sleeping bag as a top quilt and down booties or thick socks. It covers you from neck to knees (I'm 5'10").
It is pictured below with a Grand Trunk Nano. A 1.5lb Doobie Express + Nano hammock is only about 2lbs.