I had posted some pictures of a triple trailer last year. Here are some more pictures fully loaded with 3 boats and 3 Seitech dollies. It was built primarily out of 2x4's on top of a steel trailer. Two of boats are trailered right side up with 1 upside down. The boats rest on fairly long 1x6 left ripped up from a deck. Two dollies fit on the sides and one goes on top.