Miata heat/soundproofing?

[HarryB]

I know this is a lame question (and most probably a meaningless quest in a softop), but I would like some extra heat insulation in the tunnel. I have also noticed that in highway speeds, there's a lot of noise coming from the firewall behind the seats (NB2). At the same time, I do not want to add a lot of weight (or spend a ton of money) in something like this. So what people have done so far?