I would recommend neoprene rubber for the job, it's the stuff they make wetsuits out off and tends not to compress too badly. I've managed to get offcuts of self adhesive neoprene from shops that do foam matresses and cut to order foam before, if there's nowhere like that near you grab the allparts stuuf above they have a uk site as well [url="http://www.allparts.uk.com/"]http://www.allparts.uk.com/[/url]