A platform trailer neck reinforcement structure includes a first beam reinforcement structure that includes: (i) a first beam inner insert connected to an inner side of the first beam; and, (ii) and a first beam outer insert connected to an outer side of the first beam. The neck reinforcement structure also includes a second beam reinforcement structure that includes: (i) a second beam inner insert connected to an inner side of the second beam; and, (ii) and a second beam outer insert connected to an outer side of the second beam. Internal cross members extend between and interconnect the first beam inner insert and the second beam inner insert. A first group of external cross members are located between the first beam outer insert and the left side rail, and a second group of external cross members are located between the second beam outer insert and the right side rail. Each external cross member comprises an inner segment connected to an outer segment, said inner and outer segments of each external cross member of the first group connected respectively to the first beam outer insert and the left side rail, and the inner and outer segments of each external cross member of the second group connected respectively to the second beam outer insert and the right side rail.