These steps are from the guide I used (backcountry banter's), just made some adjustments on the fly.
1. Lay down insulation
2. Lay inner shell over insulation with matte side facing up
3. Lay outer shell over first two layers with matte side facing in
4. Draw outer dimensions of quilt, leaving a 1/2 inch seam allowance on all sides
5. Draw in footbox (5 inches in on each side)
6. Double, triple check measurements
7. Pin layers together just outside drawn outline, with pins running parallel to line
8. Cut along line, go slow and make sure layers aren't traveling independently while cutting
9. Use excess fabric to make two cinch cord sleeves: 1 x 44 inches and 1 x 54 inches long. Each is two inches wide. Using the interior fabric makes a nice contrast.
10. Fold 1/4 inch of each end of the cinch sleeves over twice and sew two rows of stitches to keep together. This is to provide a reinforced opening to the sleeve
11. Measure out and cut 10 x 3inch strips of Grosgrain ribbon, crease in half to make 1.5 inch loops. Add button snaps to 6 of these loops.
12. Pin the cinch sleeves, button snap loops, ribbon loops and zipper on to the quilt. Each one should be facing towards the inside of the quilt, sandwiched between the inner and outer shell fabrics. The button snap loops should be facing up/down opposite each other on each side. The zipper should be facing up if you want it to be on the outside of the quilt when zipped up and the teeth sides should face each other inside the quilt before pinning. Pin the cinch sleeves in folded over lengthwise, with the closed end facing inside the quilt.
13. Check check, double check.
14. Turn all pins from parallel orientation to perpendicular (pointy side facing the inside of the quilt
15. Load thread into sewing machine, practice sewing a sample length of all three layers together. My sewing machine preferred the insulation on the bottom layer, with a slight adjustment to the tension to keep things tidy. I didn't need a backing layer under the insulation, but some people use tissue paper/newspaper to prevent material from dragging into the machine.
16. Sew along the exterior of the quilt, check inside after each side is done to make sure things are lined up ok. Leave one zipper half un-sewn, which will provide the gap needed to invert the quilt. When sewing over the Grosgrain loops, backstitch over them to make sure they hold in securely when tugged.
17. Turn the quilt inside out, with the shell fabrics facing outwards now.
18. Sew remaining zipper half closed using ladder stitch by hand or just machine stitching depending on how clean you want it to look.
19. Thread cinch cords through sleeves.
20. Enjoy!
