Much better with trusses

The trailer structure stiffened up tremendously when switching from 1/8" x 1.5" bar stock to 1"x1"x1/8" angle, and running diagonals in every open rectangular panel.  Go figure, static mechanics from freshman year was right...

I removed the five bar diagonals using an angle grinder.  It is really amazing just how little metal is attached in a weld.  The rosette welds themselves were well-melted, but the perimeter of the bar stock is just not very much surface area.  Welding along a long edge is much better.  Even that, though, is only a small length of structure, as compared to composite structures where bonding surface area in king.  These are very different construction.

To add the angle diagonals, I measured the bevel and cut one piece, adding a rounded edge to fit neatly into the inside of the railing.

The lower side is just a right-angle cut, with the lower corner aligned to the bottom of the main beam.  This leaves two very long edges to weld along the main beam, and the clamp holds everything square during welding.

After fitting one diagonal beam nicely, it was rinse-repeat for others.  The "A" piece was used to trace out the symmetric "B" piece, transferred using a fine-tipped Sharpie line.

Cutting the bevel was a simple affair on the bandsaw with a wood-cutting blade (which is getting quite dull after cutting all this aluminum).

Rinse-repeat a dozen times...

Then after two more days of cutting, clamping, welding, and cleaning up, a trailer appears!  It's still very long, but is now stiff enough to drive a couple of laps around the neighborhood and on a rural road at 45mph.  It definitely needs a half-mile of finish welding, decking, and a lot of additional running lights on the side.  However, it is behaving properly and is not scary to tow.

To-do's include:

• running lights / reflective tape on the sides
• a "door" for the back
• decking (the 3/4" plywood fits this bill for now, but will need a coat of epoxy and then something to protect the epoxy from UV)
• bolts to hold down the decking
  
• more air in the tires
• an anti-rattle hitch stiffener of some variety
• complete welds everywhere

This upcoming weekend, my target is to install the plywood floor and the anti-rattle hitch, then try to carry the wings to a friend's house.  This would be the first real trip any part of Goat has made since moving into the garage some 13 years ago.