Abraded Romex -- almost a big problem!
'71 Overlander 27', copper conductor AC 12-2 wg Romex. Doing a little work today and happened to bump my refrigerator receptacle, which is in a 2x4 metal surface mounted box on the floor. Heard a brief "spzzzt", then the breaker tripped. On investigation, the cables, both black & white, inside the box were in contact with the metal box, and over time the insulation had worn away at a couple of spots due to over the road vibration. The breaker did its job, but the insulation is melted away for over an inch, and appears that it has been for some time.
I can't say whether this was an original factory installation, but the documentation on this old can is pretty good, and I see nothing pointing to it having been tampered with. Just a tip to anyone doing electrical work: It's never good practice to press insulated conductors against the metal sides of a box, but on something that moves around a lot, it's a very bad idea.
It's not the heat, it's the stupidity.