Ping pong balls cut in half then stacked on top of each other? Actually - same thing with the squash balls might be better in the long run. Should be easier to get the length you want that way rather than whole balls.I tried putting in two squash balls one was not enough and two raises it too much
LOL- we're starting to sound like the fishing equivalent to that 'bush mechanics' series ABC did a few years back where they were stuffing spinifex into flat tyres etc.