There's a chap on eBay sells made to measure cloth boot liners that come up the sides of the load area. His name is Ashly Bagshaw, trades as Areches, I bought a liner for my S203 from him in Nov 2008 and am well pleased with it. Can even throw it in the washing machine!
He does not currently list a S203 liner, but if you contact him through eBay he'll hopefully still have the pattern!