for retaining and supporting a plurality of rectangular deck grate panels 21 for use in erecting the bridge extending the length of the bed and pivotally secured to the bed at the trailing end thereof is a first erection mast 40 the mast includes a bracket 41 adjacent its lower end pivotally mounted to a corresponding bracket on the end of the trailer at its lowermost ground engaging end the mast is provided with a foot plate 42 pivotally secured thereon to provide a base and support for the mast on uneven ground an erecting cable 44 is wound on a drum 45 associated with a winch 46 a second mast 48 is removably carried on the trailer bed and is adapted for erection at a point distant from the first mast and at the extension point of the truss the masts are provided with pulleys 49 50 at their upper end for guiding and supporting the erection cable 44 an appropriate hook is provided on the end of the cable for engaging an eye or bracket on the second erection mast the drum and winch provides the anchoring point for the opposite end of the cable which is trained over the pulley 50 on top of the second mast the pulley 49 atop the first mast and thence the drum for storage the cable can be wound onto the drum by the winch the winch also provides for tensioning the.