Your partner isn't wrong. Heat cooks electronics from the inside out. I've pulled cameras from bags that melted their own cases. Humidity causes mold in lenses and eats away at contacts. Seal stuff in dry bags for wet heat, use reflective covers for dry heat. Forget one, and you're buying new gear.
Mate of mine left his gearbox in direct sun during a shoot in Morocco. Plastic housing was so brittle from the heat it cracked when he picked it up. That thing was straight up cooked.