For what it is worth, here is how I created my roof rack with PVC pipe. I bought two small brackets and bent them to create a hook that would fit over my first crossbar. I then attached these brackets to the pipe.
I then took the base pieces from my Yakima ski rack and mounted them to the crossbars. On the forward crossbar, these pieces are placed on the outside of the pipe. On the rear crossbar they are place on the inside of the pipe. Together, these pieces keep the pipes from moving sideways and the bracket keeps the pipe from moving back.
I purchased a goal post rack from Harbor Freight and installed two bolts on the top of the rack approximately 10.5 inches apart. These bolts stick up approximately 1.5 inches. I drilled corresponding holes in the bottom of the PVC pipe so the pipe would sit down over these bolts. These bolts thus hold the back of the PVC pipes in the correct position. Between the pipes, I just taped some foam to act as a cushion when loading the TI.
As discussed, I tie a rope between the boat and car so I can simply lift the front of the boat onto goal post without the boat rolling backwards. I then lift the back up and slide forward. It is not easy, but it works.