My buddy built a trailer similar to yours in size with the top hinged in front and he ended up strapping it down for the rest of the trip when he sheared the hinge right off the top. The only thing that we could come up with is the length of the trailer created to much shear with the side to side motion. The next trip he had it welded to the side and no problems. Hope our experience will help you.
What sheared and where? How was the hinge attached in the first place? Thanks for the comment, those are the things I want to hear so I can make a decision. Any more clarification would be helpful.