I used cheap dyna mat like stuff off eBay along with sticky backed closed cell foam.
Foam:
http://pages.ebay.com/link/?nav=item...d=251287791019
Sound deadening:
http://pages.ebay.com/link/?nav=item...d=251336536796
I added it all over the boot. The arches made the biggest difference.
I also added carpet underlay to the backs of the liners.
Made a difference to my ears!
Also make sure you deaden the saloon "parcel shelf" that way you aid to decouple the rear from the cabin.