When we had a fifth wheel the axles were arranged on the springs and hangers so that weight was more equally distributed but still if not level the rear axle will have more weight on it. When we baacked it in especially jacking it at more extremes you could see the rear axle taking more of the scrubbing.
The right side of the fifth wheel bearings were a few degress warmer than the left side also. Might have been due to crown in the road putting a slight more weight on the right side. Your temps sound fine.
If you see consistency and no problems all is well. If readings change under normal conditions then may have to investigate.