I provided some info in response to your identical post on the Hobie Forum. I'll clip my Hobie response below as well:
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You will have to check your owner's manual for the roof rack's rated capacity. The Wave manual states the following weights under the car-topping category:

• Two wave hulls - 160lbs
• Mast - 30 lbs
• Tramp and Xbars - 31 lbs
• Rudder assembly - 29 lbs
• Sail with battens - 12 lbs

(I'll leave it to you to tranaslate that to metric!)

The Xbars are at least 7 feet long, and the sail in the bag is about that long as well so if you don't have the interior capacity then they'll have to go up top as well.

I car top my Wave on the roof of a Chevy Astro van so the sails, Xbars and rudders easily fit inside the vehicle. I have backrests but they're too long and too strangely shaped to go inside so they have to go up top with the hulls and mast.

I place the hulls on crushable foam blocks that are kept in position by cutouts which align with the roof rack cross bars bars. I then cinch them down firmly and run lines from the front and back of each hull to the front and back of the vehicle for good measure. I got the tie downs and blocks at Mountain Equipment Co Op in Vancouver. It is kayacking stuff but it seems to work just fine on the Wave hulls.

Given the 13 foot hull length, you will probably want to have something in the neighbourhood of four feet ( 122 cm) between the rack bars if possible.