Mate, boxing chassis is something hotrodders do to give a bit of torsional ridgity. On a truck, you need strength, but you need flexibility. Box a chassis the wrong way and it will break, nothing surer. Truck chassis are usually reinforced by putting simmilar C shaped or L shaped sections inside or outside the origonal chassis. This isn't a 5 minute "can I do this sort of question", this is a "let me pay an engineer some big diollars", sort of question. Unlless you've spent a considerable amount of time looking at chassis that have broken, repaired them, and learnt from your mistakes, even then, you've still got to get an engineer to approve your idea. Gauraunteed, if you havn't played with this stuff before, pay someone who has.
