Weird tire wear

We've put a lot of miles on the new Elkmont recently (across the continent and back), and I just noticed that one of the tires (Marathon 15", passenger/door side) has uniformly high wear on the outside corner of the tread. The rest of the tread and inside corner is fine. The other tire is fine. The pressure is fine (50psi) and always has been (I check frequently).

There's no place inside the wheel well showing signs of rubbing. Clearances seem fine. The trailer's GAWR is not exceeded, and I would expect more of the weight on the other side anyway, with the dual batteries and water tank.

It's not sidewall wear as you might expect from rubbing against the curb, and it's very uniform, so I wouldn't think the wheel balance would be off. Last time I checked, there were balance weights on the back of the wheels.

Since I just noticed it, could this be something recent? Maybe something got stuck in the wheel well?

Or is there some other possibility?