What kind of Trouble With Tires? Tires themselves have been known to be out of round or have misplaced radial plies. Your hub/drum assemblies clearly spin freely. What do the tires (and Rims!) look like when you spin them and look carefully. Stand something by the tire, then under the tread, so you can see if lumps roll around. I've heard of breaking tires down then re-mounting to smooth them out. Every tire and every rim has a high side. Car manufacturers mount the tires so they offset. If they happen to match then the high spots become additive.
I can imagine where it's easy to end up with a bent rim on a trailer, especially tandem, too...
