2X on loading an open trailer. I've personally seen two Panteras loaded tail-end-first on open trailers, with their deck lids wrapped around the windshield during a tow. Roof repairs and deck lid hinging are especially expensive to fix. I recommend a closed trailer.
On long tows it also prevents local urchins from late-night fooling with the car or stealing 'souvenirs' at your motel. Good luck-