We once measured the temperature in a white car trunk, in the sun, ambient 70 F -- trunk temperature over 150 F !! I say over 150 F since we measured looking at a investment casting wax part - it was slumped down though not fully melted !
Keep important stuff insulated even if it's just in a styrofoam container for transportation. Remember that velocity will change too if the ammo is hot !
Heat is bad , condensation more so than moisture , is also bad .