I have a Yakima Loadwarrior roof basket that sits on the Honda roof rack (Thule or Yakima would be better choices for the rack).

Also have a Yakima bag designed to fit in that space. Have mostly used it for bulky lightweight items, such as sleeping bags.

There is another consideration: others who have measured mpg carefully find that on the Element, the empty Loadwarrior basket will cost gas as it reduces mileage by 2 mpg.

The Loadwarrior is popular with Element owners because it's among the, if not the, lightest roof basket.