In accordance with one aspect of the present development, a platform trailer includes a chassis comprising first and second aluminum beams each including an upper flange and a lower flange connected by a web. The first and second beams are arranged parallel to each other and each extend from a forward end to a rear end in the direction of a longitudinal axis of the trailer. The first and second beams are each defined with an arch comprising an upwardly oriented apex located between the forward and rear ends. At least one axle assembly connected to the chassis and includes a left wheel and tire assembly and a right wheel and tire assembly. A platform is supported on the first and second beams of the chassis. The platform includes spaced-apart left and right side rails and a plurality of extruded aluminum panels that each extend from a left lateral end abutted with said left side rail to a right lateral end abutted with said right side rail. Each of the panels comprises an upper wall, a lower wall spaced-apart from the upper wall, and first and second spaced-apart end walls that are connected to and extend between the upper and lower walls. The extruded aluminum panels are abutted in series with the first end wall of one panel abutted with the second end wall of an adjacent abutted panel such that the respective upper walls of adjacent abutted panels of the platform together define an upper, cargo supporting surface of the platform. The platform is arched to correspond with the arch of the first and second beams. A method for constructing the platform trailer is also disclosed.