My thought is this:
A down vest with attachment points and velcro on the arm holes. Close the arms and attach to the hammock for an upper body UQ.
Then consider down sleeves with attachment points and a velcro seam running their full length. When you get where you are going you open them, attach them to each other, and you have a lower body quilt.
I just wanted some HF critical thinking before I start on this project.