Hi Ted,
That condition "might" come from the toe angle of the wheels being wrong and/or the rear axle is not parallel to the front axle creating a scrub angle to the road.
Alignment issues on TT's is not totally uncommon. Some are wrong from day one. The axle can be made wrong and the hangers welded on in the wrong location. I was the lucky one to have this happen to me.
And yes, if the axle and wheels are out of alignment, 4,500 miles can grind up a tire.
While it is hard to see by the naked eye, if you have an accurate depth gage you can see a wear pattern across the entire face if one exists. Tires when made new are amazingly perfect in thread depth. If the wheel is out of alignment it will scrub in place of roll and the wear will be there.
This post may help if you want to try and check some of this yourself. There is also a link on there to my troubleshooting post leading up to the correction.
TT axle alignment & install - Detailed (long lot's of pics)Tandem axle trailers do have tire edge wear from turns in ST tires, however all 4 tires can get that.
Good luck and hope this helps.
John
PS If wheel or axle are out of alignment, it will keep wearing and kill 2 tires and then you still have to deal with it.