I feel I kind of went 'overkill' on my insulation and paid a price in vehicle weight, but I don't have any heat issues in the footbox, even when in 95+ temperatures.
Aluminum firewall skin, Reflect-O-Cool layer, Footbox fiberglass, ThermoKing foam/foil layer on surfaces outside of footbox; Koolmat on surfaces inside footbox, Jute carpet pad layer, cut-loop carpet
Paul