I've lined the floormats of my Aero (rather than sticking the mat to the tub): it works - there's definitely less road noise coming up through the floor.
You might also consider the lightweight dynamat - which is said to give most of the sound reduction without the full weight. I've used the lightweight in the doors of my i8 (which open upwards on a gas strut, so weight matters) and it's again made a difference
Will
