It needs to be soft enough or flexible enough to distort and 'fill the gaps' when the door closes. It seems like a bicycle inner tube would be the right material, you just might have to cut some thin strips and glue it around a piece of spaghetti or something. Then when the glue is dry, you can soak it in water and squeeze out the softened pasta. That's a lot of work though. Evilbay might be a better route, but this got my DIY gears turning.