Based on posts I read here, I found 'Quik Roof' at my local Home Depot
Model # QR625 Store SKU # 914563
I covered the package tray and behind the rear seat and the rear seat pan.
It stuck really well, conformed to the shape of the metal, cut easy with scissors and had no smell (like other petroleum based roofing products)
WHAT A DIFFERENCE!
I had just put in package tray and trunk divider insulation too but this stuff worked well.
I tapped on the car before and after putting the Quik Roof in place and the sound was noticeably better.
If you ever have to take your interior out, pick this stuff up to have on hand.
I think I'll take the seats and carpet out to add more to the floor pans.