I followed plans for a car hauler and bought the 5 inch channel many years back. Never got around to building the trailer until I retired. Then the requirements changed some. So, to beef things up I bought some 3/16" x 5" flat stock and welded it to the inside of the channel (except where the channel overlaps). I also added a third member 2 x 4 .120 down the middle. Cross members 1/4 3x4 16" o/c, decked with diamond plate I bought several years back.
6K axles, brakes and heavy tires. Cummins pulls it fine and the first voyage was a Ford 9N with a backhoe and FEL on a 600 mile journey. Trailer has a 2ft dovetail.
Have not weighed the trailer dry so I am not exactly sure of the tongue weight. I suspect I am a little heavy especially since I have a 80lb hoist to mount yet. Sides are next
I would like to post my 14ft enclosed later for comments.
Conversion of a 13 ft trailer to a dump on the radar scope.
First picture post, hope it worked