I know that this is a very old thread, but others may find this information valuable.
As you know, the primary contributor to heat in the vehicle comes from the exhaust tubes in the tunnel.
You can install a heat barrier (there are many types) between the floor / tunnel sides and the carpet, but this adds bulk to an already space-challenged situation, and eventually the insulation material heats up and begins to radiate heat on its own.
You really need some method for removing the heat mechanically.
If you take a look at where the mufflers and cat converters are located, you will see that GM has installed metal heat shields that are spaced away from the surface that they are protecting.
The air space allows for a mechanical removal of heat (as the vehicle is driven) instead of attempting to block the heat with insulation.
So, following the GM engineered model, I crafted an aluminum plate to surround the exhaust (on three sides) while still leaving a 3/8" air space between the plate and the tunnel sides and the tunnel closeout panel.
Designing the plate and having it fabricated was a little tricky, but there is adequate room if you measure carefully.
I took heat measurements at the base of the tunnel before and after I installed the shield and I measured a 30 degree heat reduction under medium load conditions (driving in hilly areas) and a 20 degree heat reduction when cruising (flat roads).
If you are interested in more detailed information, send me a PM and I will share more.