I don't know diddly squat about tires but I'll throw in one bit of info for consideration and Ron may be able to expound on it a little further. We have the sensor for our weather station stuck up in the top right corner of our rear bin. It FREQUENTLY registers over 100 degrees. I know tires can take heat but to be somewhat continuously baked might affect that tire. Ron, don't you have your weather sensor inside the spare tire cap? If so, what kind of readings do you get when you are out camping and the sun is hitting the tail of the PC?
Tire guys - would this matter?
Yes I keep the indoor thermometer's outdoor sensor in the spare tire compartment, wrapped in a rag & placed in the center tube. The heat of the day with sun beating down, it will read a little higher than ambient, but rarely more than a few degrees. Our cover is painted gray/silver. Maybe it reflects the sun better than some of the other painted tire covers.
For the record, I typically keep 70-75 psi in the spare, anticipating some amount of heat build-up in there. 70-75 psi is more than any of my road tires need. I did figure on letting out the right amount of air if gone into service. I do consider that my spare might loose some air over time, not having enough for an actual emergency.