Do "vented" tailgates help on 5th wheels?

Our Place wrote:
Friend of mine says he gets better mileage with a vented/louvered tailgate. Do they really make a difference or is it just another novelty item that's nice to have but not needed.

He might as all rigs aren't the same.
I've used them on four different trucks pulling my GN trailers and 5th wheel RVs.
I towed the first 5th wheel RV with out a tail gate as it cut turbulence in my trucks bed. Bought a Custom Flow steel gate. Now I still had a gate with louvers to let wind turbulence out and a V notch to help hook hitch and un hitch easier.
Never considered them as a fuel saver simply because it wasn't advertised as doing so.