Hello Bob,
We just got back from a 6000 mi trip, to the East Coast and I too watch my temps on my axles and tires. I use a hand held Pyrometer. You can get these at a lot of different places, like Sears, Radio Shack, etc. I bought mine from
www.tooldesk.com
They range in price from about $30 and up. Mine was about $70 with lazer sight. When I take a break I shoot my wheels right between the lug nuts and shoot the Tires on the side wall. You'll be able to establish a base line and then watch for elevated temps. My temps run about 110 deg to 125 deg. I also run my air pressure at 65 psi. on the TT and 65 front and 80 rear psi's on the Truck. Measured cold. There will be as much as 10 deg. higher temp's. "On The Sunny Side Of The Street"
The Pyrometers are great RV'er Tools
Happy Travels