I was pulling a long-ish (28') camper with my Expedition. I hated the 'pull' of semi's, so I got a Hensley Arrow. Fixed everything except for not having enough power, but that's another thread.
I was having a HECK of a time with the tires that came on my camper. They wore AWFUL on both shoulders. I checked the pressure time and time again. It got to the point that I needed to put on the spare just to get home one trip. When I got home, THAT tire was worn on the shoulders visibly.
Funny thing is that I couldn't find the time to get the trailer aligned (or anyone to do it...), so I got new radial tires before I left on a particularly long trip, hoping they would help/last.
That was 2 years ago. The new tires still have absolutely no visible wear even though they've had probably 5k miles put on them.
Curious: Do you tow with a full water tank? I did that once and it had a significant difference to the rate of wear on my tires (that was the trip where I had to break out the spare).