I haven't used my Featherweight to quilt, but I have used it to topstitch bowl cozies, which is probably the same thickness as your quilt. I increased the stitch length considerably and it worked fine. I did have to use a folded up piece of fabric to make it over some of the seams (like the dart), but other than that, the Featherweight worked like a champ.
Use a practice quilt sandwich to find the right stitch length. Let us know how it goes! Gotta love the Featherweight!