We used that silver backed heat insulation padding under the carpet of my dads MGB.

Fred, Speedway motors sells some insulation that is use in the roundy rounder cars for long distance racing, it is like dyno mat but not as expensive dynomat Give them a call or check them out on thier web site

Or you could just start racing in the winter

I used 1/8 alu plate , I bent it to the inside of the tunnel and spaced it off 1/8 and put kevlar mat inbetween , it was built for transfer case explosions and works good for heat too