Dean, I've PM'd several people whose building experience I respect and have decided what I'm going to do is build the lightweight frame as shown in Andrew's pdf drawing. But I'm using a 2x3x 3/32 tube for the front and back tube, and 2x2x3/32 for both sides and the center cross-member. Then I'll use 2x2x1/8 tube for the tongue...........with 2x2x3/32 braces for the A-frame on the tongue.
As a custom furniture builder, I am a firm believer in the strength of an enclosed "pod" such as the tear body...............especially when the pod is built of a material as strong as plywood. So I think a properly built tear body on top of the frame I've decided to build will provide a trailer which will provide years of use.
Now that that's settled, I have the period of time between now and when I start building the trailer to change my mind about 50 more times!
