Simple enough job , I did mine with 3 sheets of marine ply so it ended up almost 2" thick, it also gives you the oportunity to clean off and Hammerite the cross members , you can also have a good look at the backplates on the brakes , always a bit rusty. If you look in yellow pages for car trimmers and car seat refurbishers, they usualy stock the ribbed rubber matting in big sheets so you can do it all in 1 hit, or get the liquid rubber stable flooring pour on stuff.