I have never fitted or owned a roof box, however, I have always considered them to be a universal fitting which would adapt to almost any roof bars. A quick check on e bay reveals that there is someone selling genuine lexus CT200H roof bars for £138 so my view is that a deturmined individual would be able to fit a roof box despite the various retail outlets seemingly not yet marketing bespoke roof box kits. The roof bars literature, being genuine Lexus ref no PZ403-Z0610GA ( as quoted in the ebay ad) would advise as to what the maximum recommended total safe loading would be Hope this helps

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