The inside front passenger area gets very hot in the summer. Especially when crawling in a cruise! Right now there is some of the original insulation on the firewall. Some is missing, and falling off. What are some materials to use, to help stop the transfer of heat, from engine bay into cabin? Though about using foil backed fiberglass insulation. Just like the material used in home building. Batt type insulation. Does this sound feasible, or any other material better than others? Thank you in advance.