I cannot advise on how to install the roof rack, because I drove to Necedah to have mine installed by the experts.
One thing I did realize after the fact, is the Yakima crossbar length does make a difference. Originally I ordered 60" JetStream crossbars. These fit the towers (right on), with no overhang beyond the vertical sides of the camper.
Initially the roof rack was used to carry a Yakima Skybox 12, with holds a large tent and other bulky items. The Skybox has four clamp-like attachment points, which must be inside the towers on the 60" crossbars. The width of the Skybox limits the height the fantastic fan could be raised (opened). The fan works, but cannot be opened more than about 3 inches.
After a year or so I purchase a kayak and needed to add Yakima J-Hooks to carry my kayak on the other side. Because I wanted the full opening of the fantastic fan, I ordered Yakima 70" JetStream crossbars to replace the 60" ones. I'm now able to secure both the Skybox and J-Hooks, with one side clamped on the inside of the Yakima towers and one side on the outside of the towers (where the crossbars overhang 6 inches beyond the vertical side of the camper. My travels during 2019 were extensive (12,000 miles with the trailer being towed) and no issues whatsoever. The Skybox and J-hooks clamp securely and have never required adjustment. Also, I have never hit my head on the crossbars, Skybox, or Kayak. The overhang is 6 inches, and my body isn't that close to the camper, so my head isn't either. There is no interference with the fantastic fan.
This seemed to be the thread to mention consideration of a 70" crossbar rather than the 60" which fit the width of the camper exactly.
