I don't know where this is but it doesn't sound impossible to me. A quick Google shows that the FDA recommends 160 F for casseroles and that in direct sunlight a car can hit 160 if the ambient temp is >105 F. I know mailboxes aren't cars, but over a longer period in a smaller metal box, it seems like the math could check out
I live in Utah where it's been sinfully hot and dry for the last week. I fully intend to test this theory. I just bought a high temp probe that should get here tomorrow. I will provide an update once the testing has been completed.
I don't know if this could inadvertently dox you but I'd be curious to see an hourly outside temperature too to see how much hotter a mailbox gets than outside. Based off your first graph here I'm wondering if cars having glass windows makes a greenhouse effect that would make a car hotter than a mailbox, everything else equal?
Seems like a worthwhile thing to do! I'm not worried about doxxing, since someone would have to go to pretty extreme measures to correlate with the exact climate where I'm at. I installed the sensor after the hottest time of day had already passed, but here's what it looked like:
I'm pretty sure the spikes in the mailbox temperature were due to cloud cover.
In my opinion this pretty conclusively proves that you can't make a mailbox lasagna. This is the graph I looked but for my previous statement:
And it shows that a car can hit 130-140 at temps around what you posted. Which is so much wildly higher than what you posted I do have to assume cars have some sort of greenhouse effect going that mailboxes don't
Finally when you consider how much of the total volume of a mailbox a lasagna covers, I have to imagine that'll slow heating down even more! Great work!
I have it positioned right now so that the probe tip isn't touching any metal, but I'll probably add a bit of foam. I have some incredibly irritating foam packing peanuts that would probably work well. I'll go do that now.
EDIT: here it is, in all its gloriously crappy, uh, glory: