If it is too hot to touch it is too hot to leave. Oh sorry that was from Smoky the Bear but does apply to the trailer hubs.
As for not needing to touch the hubs as you do not do that to the truck hubs.
When was the last time you saw a truck or car on the side of the road with a bad bearing?
Now when was the last time you saw a trailer on the side of the road with a bad bearing?
I see trailers almost every spring. Can't say I have ever seen a car or truck.
I also check all tires including the truck at each rest or fuel stop with the good old hand.
Consistent temperatures on each axle is the key. I have found the sun has very little effect (side to side) as there is a 65 mph wind cooling everything.