After messing around with the no-sew DIY poncho liner under quilt (PLUQ), I decided to finally sew it up for good. The problem with the no-sew version was that it often got tangled up with all the extra tie-offs. I've now sewn up a few PLUQ and have had great success in adding extra insulation to the mix.
Pleats, Darts, or Shock Cord?
This project isn't terribly difficult with moderate sewing skills. The most challenging thing is sewing the darts, or pleats, to gather the ends, but this step can be skipped if instead you run shock cord through the end channels and use a cord lock to cinch up the ends. I have a version that does this, but I found that the material and batting in the poncho liner makes the ends a little stiff and difficult to gather. Using darts/pleats have worked very well, but it doesn't allow you to modify the enclosure in the field.
Using pleats instead of darts allowed the fabric to billow and provide a little more area for insulation.
You can get as fancy or as simple as you want. On one PLUQ, I didn't fold the material exactly in half, making the side touching the hammock shorter than the outside, thus creating a baffle where I sewed in some extra insulation. This created an air pocket between the layers of insulation. This wasn't any more difficult to sew, but it did take a little extra planning.