NX 250 underquilt
I use the Clark Z Liner,then my Incubator under that,clipped into position to the hammock and then when it's really cold,I put my New River UQ under all that as well.
I carry it all inside a Lazy Slug Tube ,which I lug around in the back of my 80 series landcruiser
All this usually goes under my WBBB superfly
The Clark isn't the flattest lay (that would probably be my HH safari deluxe or the 72 Dangerbird) but it's by far the warmest cold weather rig I've got.Underquilts attach easily and don't roll off your shoulder and combined with the Overcover zipped in place ,it's brilliant.