Yeah, well, this is actually why I still (after 8 odd years in a hammock) do not own an underquilt

I keep coming back to using my closed cell blue foam pad in the hammock, I have nice wide ones, not the standard width, and then I rig my silponcho underneath it like the "garlington insulator" method - it's basically a windblock and airgap which I can stuff with things to give a bit of insulaiton, like wadded up space blankets, garbage bags, or in very cold weather, another sleeping bag. most of the time I only carry the space blankets and poncho. In colder weather I carry usually a hammock shaped wad of cheap polifill insulation from wal-mart sewing bin and stuff that in.

nice part is I can go to ground, poncho is lighter than an underquilt (by a lot) and multi-use.

But I do have lots of trips where I can not hammock for the whole trip - no trees in some places!: