Remove tire from trailer, then grab a bucket, add 2 tablespoons of liquid dish soap,
half fill with water. Pressurize the tire, pour soapy water all over the tire and rim.
Look for the bubbles forming over the leak. Puncture, valve, pinch, pitted rim
doesn't matter, soapy water and the resulting bubbles will show the leak.
Once you know where the leak is, it's easy to solve the problem.
BTW, I can't see where the hub or bearings could cause the tire to leak
unless the hub was improperly mounted so that it scrubbed tread off the tire.