Here is what I do (or did). First of all I weighed my rig (combination) when it was loaded and ready for the road, including full fuel and passenger. Then I made sure I even had the correct load range tires on both my truck and trailer.
Next I order a TPMS and installed it, which takes about 10 minutes and $200+ to do.
Based on my weights and ratings I set all my air pressures during the morning hours when the temperature was around 70 degrees and all the tires were in the shade.
Then I just sit back and enjoy watching my TPMS. It is the only way to really know what your tires are doing as you tow in different conditions and at different speeds.
