The first thing you need to do is fold the poncho liner in half the long way. Take a 96� inch long zipper and measure where the zipper will start and end on the liner, mark it with a pen or a couple of pins. Separate the two parts of the zipper and sew them into the left and right side of the poncho liner. Using a sewing machine is best but, you may want to goto a sewing shop and price it out.
You can also add a draw string at the top of the liner. Simply poke two holes at the two top corners of the liner�s seam, then take a straightened metal coat hanger and tape the paracord to the end of the hanger. Feed it through the first hole inside the factory stitched seam until it comes out on the other side. Tie a large knot or get barrel locks to keep it from pulling back through. You can roll the liner together with the poncho and strap it to the bottom of the buttpack back pack for a lightweight shelter.
If you want to add a zipper instead of snaps you can try the following:
