I haven't been inside the drivers side of the divider, but the trunk side dosent have much covering it and the tank....just the thin black material you look at when you open the tailgate.... It comes out very easily...

I would take a good look at what is under the people side and what you might be covering if you foamed it up.... some removable foam/deadener wouldnt hurt anything though....

There have been a couple of guys that have done extensive work on deadening the outside noise on their car..... the rear wheel wells, styrofoam area under the rear mat, between the license plate and cargo area, door panels and I believe the floor/firewall too... using dynamat or similar material... maybe even some in the hatch itself...