Originally Posted by sonoronos

Using 1/8" particleboard, I cut a sheet out the same size (slightly undersize actually) as the fabric floor cover in the rear cargo area. Then I bought 1" thick urethane foam sound absorbing material (the same stuff on my hoodliner) with one sticky side and attached 1 layer to the top side of the particleboard and 1 layer to the bottom side. Total thickness = 2.125". Place underneath the fabric floor cover and it cuts out a lot of the road noise inside the car, especially at speed.

This is much better than Dynamat, cheaper, and reversible.

I'm not sure what you can do with the box between the cargo area and the seats. Access is needed in there, so a permanent foam fill would be ill-advised.