

Pin the pattern on fabric and cut two. These are your sides. Next determine how wide of a support you need. Your call for your needs. Remember to figure in your seem allowance. If you sew with 1/2 inch seams, add an inch to what you want your final width to be. Cut a strip of fabric the width you want making sure you have enough to go all around. If you can find a wide rip-stop fabric, all the better. It is tough and will take abuse yet easy to sew. Denim would also be good but not really a heavy canvas.
Double and sew about 2 1/2 to 3 inches at the beginning of your strip. Sew a couple of reinforcing seems. This is where one piece of velcro will go. Don't run your velcro full length into what will be the seams. Pin to one side...right side's of fabric together. Straight stitch around, remove pins and sew a reinforcing zig-zag directly over the stitch line or another straight stitch just a little apart.
Once you have a general idea of where the strip will end, you can cut leaving enough to double at the end and reinforce for your second part of the velcro attachment. These two will overlap. Turn right side out, sew on your velcro.

Another advantage to this method is if the cover needs washing, empty the rice, remove the bag, wash and refill.
I am working on a little more well defined design but the "slouchy" design is super easy and works very well with minimal sewing skills.