We often use the NSX as our grocery getter and, yes, the trunk can often get warm enough to slow cook certain things when the gas motor is on. Since we're in CA, we are required to bring our own grocery bags anyway so we often try to store any temperature sensitive items in insulated bags to keep things cool. We have a fold-up insulated container we had used in the GT-R due to the heat from that car's exhaust but it's a challenge to fit in the trunk of the NSX. If you can find one that fits, that might be another idea.