1) Buy a pack of Chicklets. Those white chicklets in a yellow box. Those are exactly 1/35th scale.
2) Put the Chicklets in bowl of water. Leave it for an hour or two. The water will dissolve the hard candy covering.
3) Wash the remaining squares. Let dry for a few minutes.
4) Round off the bags by lightly pressing the corners. Then, dab the sided with the pointed end of a hobby knife to simulate stitches.
5) Press a rough cloth or fine screen on the surface to provide texture.
6) Place on surface and bend according to shape. Let dry.
7) Paint and weather. If you want to make a hole, just stick the point of your hobby knife in the sandbag and chuck out a rough hole. Don't worry about ants.
The gum base of chicklets is not edible. It's only the hard candy coating which attracts unwanted insects.
The gum base also dries rock hard as one can attest to dried gum under the school table. http://www.armorama.com/modules.php?op=modload&name=SquawkBox&file=index&req=viewtopic&topic_id=60506&page=1