I carry an "infrared digital thermometer gun" which you can get from Ebay for less than $10 delivered. At each stop I check the temperature of the brakes and hubs on all 8 wheels. This gives early warning of loss of air pressure or binding brakes. I also use it when adjusting brakes, ensuring that all the wheels on the trailer are within 10 degrees after heavy test braking. This gives me peace of mind on a long trip.
Nick Crowhurst, Excella 25 1988, Dodge Ram 2500 Cummins Diesel. England in summer, USA in winter.
"The price of freedom is eternal maintenance."