Ware on both outer edges of a tire indicate under inflation. Have you ever weighed the trailer and used the inflation charts to determine the correct pressure?
Ware on one side of a tire may indicate axle misalignment. i use an 8 ft florescent light bulb across the center line of the tires. The bulb should touch all surfaces. Any gap on to one of the tire edges indicates the misalignment.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles