Sometimes I stack my 20* underquilt and my zero* underquilt. I install the 20* underquilt first, closest to hammock. Then I add the zero* underquilt last. It’s on outside. The zero* underquilt is up tight to 20* underquilt, this reduces some of the loft in 20* underquilt, but then, chances of drafts and air gaps are slim and none.

And as mentioned, you and your husband can check setup while one is in hammock and other checks for gaps, adjusting as needed.