While I do believe that stuff needs lubrication, sometimes we can do more harm than good. The only bearing/hub failure I have personally had in 40+ years of driving/towing was my own fault. I was young and did not really know what I was doing and tightened the nut too tight and destroyed a bearing. I learned a valuable lesson that day.
To answer the original question, I look at the hubs on my utility trailers and if I have no reason to suspect anything is amiss I leave them alone. I have only had my
Scamp a year and half and put a new
axle under it when I got it. I checked the
axle for grease when I got it and have maybe put 5000 miles on it since. I may check it next summer before we leave on a long trip but this
Fall, Winter, and Spring will just be short, semi-local camping trips and I am not worried.