My 2017 StumpJumper is the same color as your Cayman, and your bike is the same color as my Cayman You have great taste. ;-)So I recently bought a Seasucker Talon suction bike rack. After doing a test with my brother following me in an F150 I drove with my bike from Toronto to NY. I stopped every 150 miles or so and there was no loss of suction.
Note: To clear the spoiler in the raised position, you need a spacer on the rear wheel mount, but for now I was able to keep all the suction cups near the edges of the roof and the rear wheel just under the rear windshield, which prevents any load on an unsupported portion of the roof. I only took one picture before I had placed the rear wheel cup far enough down but basically mounts like this:
I might go this route as I mountain bike every Thursday in Park City after work. Would be nice to take the Cayman instead of my '18 F-150. Gas ain't cheap!