It's a predicament as old as backpacking itself. You need to hang your damp sleeping bag out to dry, but the drizzle won't quit. What to do? String up the soggy sack inside the tent with handy straps sewn onto the shell. Either do the stitching at home before your next trip or bring a needle and thread with you in a zipper-lock bag for a rainy-day tent project.
Step 1: Cut a length of lightweight nylon ribbon or shoelace into three 10-inch segments and sear the ends with a lighter.
Step 2: Fold each ribbon in half, bringing the ends together. Place ribbons at the bag's head, middle, and foot. Using polyester thread and a medium sewing needle, stitch each ribbon at its fold to the shell on the bag's zipperless side. Be sure to stitch along the existing side seam to prevent damage to the shell, and avoid stitching into the down or fiber filling beyond the seam.
Step 3: Finish the fastening job with three or four snug loop stitches thrown across the width of each ribbon. If feathers are leaking through the thread holes, dab seam sealer on the holes.
Step 4: When that rainy day arrives, suspend your bag by tying it to guy loops in the ceiling. Keep the tent windows open so moisture can escape. When the sun comes out, use the same straps to secure your bag to an outdoor clothesline or tree branch—or hang it between two firmly planted trekking poles.
A minor modification such as this shouldn't affect the warranty on the major components of a sleeping bag (such as the zipper, loft, or general workmanship). If in doubt, check with your bag's manufacturer before threading the needle.