Aside from what Mitch said, I think you would probably need a lot more shielding to significantly reduce noise/vibration in the cockpit. There are plenty of other transmission paths aside from the firewall. The cockpit is as noisy as any other aircraft, but I've never noticed any heat transfer through the firewall or excessive vibration. A decent headset will fix the noise. As for heat transfer, being in NZ, you will probably want all the heat you can get.

I was in NZ for Warbirds over Wanaka in 2018. Met some other RV-12 builders. Very impressed with the Lake Taupo area.