Uneven tire wear

I've been researching this forum for tire advice. I've learned quite a bit about tires and rims. I'm planning on buying a set of Sailun ST235/80R 16/14 S637T from Les Schwab. I believe my 8-lug Sendel aluminum rims are rated for 110psi. I will double check when the rim is off. I must cop to being very unobservant regarding my tires. I HAVE noticed that the front right tire was nearing replacement wear (probably because it's closest to the steps/door so I see it clearly), but I didn't notice that the wear was uneven with considerably more wear on the outboard side when compared to the inner side. Upon checking the other 3 wheels I see the wear is not that bad, comparable to the inner side of the front right tire. I'm prepared for the lecture of needing to be more conscious of my tires, but what would cause the wear pattern I've described? Can trailer tires only be "rotated" front to back and not side to side as with autos & trucks? Any experienced advice will be appreciated.

Montana High Country 34' 5th wheel