I bought the mat stuff today - it was actually $15 a meter, I must have remembered wrong, but it was 6 foot wide roll and I bought 3 meters of it, so for $42 I'm doing the whole car and I'll have spare to double up in areas.
It's 1cm thick and I'm going to do the whole rear deck. Will cut down on a lot of road noise that way. I'll work it out I'm sure. Can't be too hard.
I'm more worried about the wheel arches at the moment but I guess I'll suss that out soon too.