United U-Series Cargo Trailers like all United Trailers come with five year limited warranty backed by three generations of manufacturing experience, superior materials and durable designs. Unique features include the rear corner posts and header which are made of 12 gauge steel to provide the ramp door with a solid framework. You can also customize your United U-Series Cargo Trailer in many ways and choose from different floorplans, nose shapes, and colors. The Cargo Trailer 6′ Wide 3500lb Tandem Axle above has a prive of $2,999 just to give you an idea. Ultimate Trailer.