Both will cause it. Toe-in can be checked with a straight edge across the wheel on the trailer ( 3 & 9 o'slock) and measure the distance of the rim front and back to the frame. Should be the same. camber can be checked with a level from top to bottom of the wheel mounted on the trailer ( 6 & 12 o'clock) on level ground. Should be level. If it is a solid axle, the problem most likely is toe-in. If a torsion suspension, it could be either one.Toe out will cause this too, wouldn't it? Not just camber