Brought one of my Poke boats back from Florida on top of the car.  Used a foam pool noodle, cut in half crosswise, to raise the kayak up off the roof of the car and lashed it down with two tension webbing straps and tied down with small rope on front and back to cut down on any sideways movement.  Worked like a charm the entire 2000 miles and at 70 mph speeds.  Cost a whole $1.00 at the Dollar Tree.   8-)