You will need something, an asphaltic base material like Dyna Mat on the trunk lid, the quarter panels and doors if for no other reason then to stop the drumming, Dyna mat type products are to reduce resonances while the stuff Henry Rifle (Jack) is installing is also a heat reflection material as well. Generally with Dyna Mat you do not need to cover entire surfaces - only enough to reduce any vibration (change the resonance frequency). You will still need to put at least some insulation on the floor and on the firewall, especially with a roadster, to reduce heat from the engine, exhaust, and reflected heat from the pavement. Some reflective insulation on the rear quarter panels can be considered as well. Most of this reflective stuff, at least the good products, is a fibrous ceramic with a foil covering. You can buy self stick or use contact cement which is the easiest to fasten it in place.