I have a triple-axle trailer. Over the last 3 seasons, I've rotated the tires to all 3 positions on the same side. All tires are wearing equally and look good. Now, I'm left wondering if I should keep them on the same side or switch sides. Any suggestions?

Unless you see one side wearing faster than the other, I would not rotate them side to side.

I have never thought about this. I guess depending on mileage and such not so sure its necessary. for me at least for the amount of mileage i put on them, tires will sun crack before they get uneven. Seeing as my trailers tires arent balanced anyways doesnt really matter.

I have to tow 100 miles round trip every time I use the boat. Plus, I usually have one long trip. Last year I went to the LOTO shootout.

Bias or radial?

Radial

Just go front to back if radial, even though I have never seen it, but supposed to cause beltshift if you switch rotation.

+1

I also hear that the face of the tire feathers in the direction it's rolled and turning them around makes that feather go in the wrong direction.

Why do you change direction when you rotate the cars/ truck tires?

IMO,
If all the tires look even, I see no reason to swap locations as your axles apperantly are aligned. Swapping tires around is a bandaide fix for axle misalignment. A leafspring trailer will have equal weight distributed to each wheel, so I see no reason there either.(Torsions are a different animal and don't apply)
If one wants to suggest the front wheels are wearing do to scrubbing more on turns, then you are spending to much time driving in circles.