This is a perfect place to carry about half my stuff... But - I know how twitchy you guys get about leaving your kit in a hot car, so I decided to tamp some myths..
It is without dispute that this box, when it was colored Black, was almost as hot as a pizza oven on a sunny day. A black box make a great solar collector. I wanted to change that...
People think anything reflective, like Silver, is ..well; 'Reflective'. It reflects light, if that makes you feel better... I used this silver because I was shooting a 8M rowing shell at the same time, not because it was the best choice.
White would be the best choice. White has the least pigmentation, which absorbs fewer Infrared rays than any other color. Silver is little more than shade of Black with a given percentage of metallic particles mixed in.
Still, I wanted to see what was going on. I have recorded temps in aircraft with a variety of coverings, so this was pretty simple. The heat of the day peaks about 2pm on average..
At 2:15 the ambient temperature was 83f - 28c ..and the winds not strong enough to fly a 2M trainer ...
The most exposed surface temperature was 108f - 42c ... of the objects inside, the hottest was an orange skimboard at 115f - 46c ..the least hot was a harness at 93f - 34c. (everything inside had been sealed within for at least two hours prior - there is no ventilation.)
It is the temperature of the inside of the lid that means the most to stuff on the inside... The lid is made of some sort of vacuum-formed plastic and is quite dense. It is only about 3mils thick which is good... The temp inside the lid was 132f - 55.5c
One reason the outside and inside temperatures vary is that the breeze, however light, pulls the heat away from the outside. The inside air is dead calm.
The reason the skimboard was hotter than the harness, was the skimboard is quite dense and the foam-core harness less so. The harness cannot hold heat as well.
If you lived in an area of really high heat - it would be best to line the underside of the lid with 5mil of closed cel foam. The lid currently radiates heat to the objects in the box just like an electric space heater . The foam would dampen that.
And yes I leave kites in there pretty much all Summer. I open the lid if it is really hot.