James, I would also recommend the cargo net made by Yakima for their Basketcase roof top cargo rack. I have a Basketcase cargo rack for my VW Jetta Wagon as well as the cargo net, and the net is just the right size to also stretch across the back cargo area of my gwagen. The net is bright red and made of thick sturdy stretch cord with hooks all the way around the outside of the net. You can pick one up for about $20-25 online or at your local bike shop or sporting goods store.
If I get a chance this weekend, I'll string it up in the back of the G and take a picture for you.