Hoops are 3/4" x 10' long, Grey PVC, electrical conduit pipe. Each hoop is made from two 10' lengths. One end of the pipe is flared to form a socket, the other is straight. Kevin stuck the straight end into the socket end, without glue, to join the two lengths together.

Photo of flared end of pipe.

The top backbone is 'wire-tied' (zip-tied) to the hoops. In the following photo you can see the plastic ties used to secure the loops to the backbone

The free ends of the hoops are just stuck inside the trailer frame. So far they're held only by friction, no securing. Although, the cover is tied to the trailer frame and that would help to hold everything down and keep the hoops from popping out.