Take the tires to walmart - about 5 bucks to balance and it will give longer life to your tires..Legally speaking, the trailers are supposed to have ST tires on them. If you have an accident with the trailer and the accident investigator determines you had auto tires you are at risk of not having insurance pay out.
I used to own a company that manufactured trailers and the poster above suggested that the trailer axle alignment should be checked to prevent uneven tire wear. He is absolutely correct. A lot of trailers are just thrown together with little regard for accuracy of alignment since the welders are paid by the number of trailers they produce. At our company we used a jig to ensure the alignment was dead on. Our guys could generally weld up a 5 x 10 in about 45 minutes and have it on the line to the paint department.
The best way to check alignment is to measure from the center of each axle cap to the center of the coupler end that goes over the hitch ball.. The measurement should be the same for each axle cap to coupler end.
The biggest issue to address on an annual basis is to remove the hubs, clean your bearings and repack. I see trailers on the side of the road all the time with the axle burned off and the tire laying on the ground. That my friends requires a whole new axle
Good luck in your trailer endeavors.