Dynamat sounds good! Looks expensive tho... I would be running it down the passengers side fire wall and a little on the floor...

If the inside of the car gets wet, how do I dry underneath it?

jaycar do a similar product @ $30 for a 900 x 330mm sheet & can do group buys http://www.jaycar.com.au/productView.asp?ID=AX3687

If the jaycar product is still relabelled "brown bread" brand, It has a much stronger smell and less tackiness than dynamat, especially when exposed to water.

Josh: I've got double layers of dynamat xtreme on my passenger side floor and firewall. And a single layer inside the remainder my my entire cab. Floor and firewall also have a layer of dynaliner over the top.

It's enough to step any feeling of heat from my exhaust.
I've drowned the car a couple of times in fresh water since applying it. I cut a section out to inspect the floor a few months back, there was no sign of any retained water.
It's all about how well you roll it in the curves to seal it. You can also get dynatape to seal the edges if you're paranoid.

I spent a few years as a pro audio installer at a reputable workshop. After using most brands available dynamat is the only one I'll recommend.

Haha yeah, I was looking at a set of 30x9.5HT's the other day to cut down on tyre noise...

But to be honest, who knows, I might never even feel there is a difference In the heat and this could of all been for nothing