With an infrared gun you should be able to shoot the drums after a high speed brake event and compare. If one is significantly higher temperature than the others a brake adjustment may be in order.
I am retired so every long trip I do I allow at least one extra day for the trip.
I start my long trips with about a 25 mile run using the brakes as little as possible. At the end of the 25 miles I do two things.
First check that tire pressures on my TPMS are balanced. Every axle should have the same pressure assuming the pressures were balanced when tires were cold and no sun exposure.
Second after coasting to a stop with little to no braking I check the bearing hub temperatures. Be sure to have any decorative covers removed. If I find a hub temperature much higher than the others I return home and repack the bearings along with a very careful inspection of the bearings and brake assemblies.
If you can not afford the extra day for a long trip I suggest taking the trailer out for a 50 mile run the week-end before a long trip.