I also have the Thule Motion XT XL. We go skiing a lot and camping (dont do any real off roading) so its nice to have the tons of extra cargo space. I use it currently with the stock cross bars moved all the way forward. The box touches the antenna slightly but isn't such an issue for me; I probably could add cross bar pads to eliminate the touching but again not a big deal for me. The box also touches/interferes with the lift when open but again when you are conscious of it you just need to gently open the lift so you don't scratch the rear spoiler or damage/scratch the box. I recently purchased a full roof rack which should allow me to move the cargo box forward another inch or so and solve just about all of my problems. Happy to take some photos if that helps your decision making process.
