I have a 6x12 dump bed box with 3" c-channel crossmembers. I would like to build a trailer frame for this and weld the bed to the trailer frame, no dump, for a utility trailer. I have a question on how to build the frame. So this bed will be welded to a 5" channel frame and my question is would I need any crossmembers in the main frame or will the crossmembers welded to the top be enough?