I did my floor, roof and inside the doors as well as trunk with rattle trap, good stuff on ebay, but you can use what ever. Even with out the interior in did a temp test and there was a few degrees different but if yoy put full interior then it would drop more.
If you go with one of the 'mat' products (ie: not spray-on), I'd recommend going with one of the butyl-based products rather than asphaltic-based. The asphaltic-based stuff is more prone to melting/detachment due to high temps, not to mention the increased 'stank' factor.
You'll find that the butyl-based products cost a little more, however.