I have the same tires that came on the trailer in 2005. The first sign of wear was on both edges of the tires. Not enough air? I went from 45# to 60# with no change in the wear. Everyone I talked to said not enough air. So I went to 70#, now the edges are cupping as if the trailer is bouncing. I don't see or feel any bouncing when hauling it. I'll put a pair of Radials on it before hauling it again.
Custom Springs in Memphis said I need another axle, to much weight for 1 axle. Bring them the empty trailer, they will configure the 2 axles to the trailer, add 1 and double fenders for $400.