The 5 x 16 trailer frame will probably have to be a custom build Mike. I just got curious and did a search and the closest I could find is 6.4 by 16 and that had rails and a drop ramp. The guys on the corner could probably build you one. On second thought you might find a boat trailer close to that size. Can't wait to see what you're gona put in a trailer that size.
GAry