My use for a wireless thermometer was not to measure the outside temp., but rather to monitor to inside temp of my freezer compartment of the trailer. I usually travel with the fridge
off, and on long runs on hot days, wanted to ensure that contents would not thaw. I was able to monitor from my tv, and found the readings to be quite accurate.
My Toyota 4Runner has a factory outside temp guage, and the receiver is mounted somewhere behind the front bumper so it is out of the wind and direct sun.