Either I am not up to date on underquilt technology or you aren't up to date on the better pad offerings. The under quilts I have seen have all been over 20 ounces. Most seem to weigh about twice what a 20x72 Neoair Xlite weighs. Not sure how small they pack, but the neoair xlite packs to 9" long x 4" diameter. The underquilts I have seen also tend to cost about twice as much as the xlite.

I have to wonder if it wouldn't make more sense to just use an Xlite and have the option of using it on the ground when needed.