When towcar in trailer I have always been told to put in neutral while towing.why not park leave in neutral while tie down when everything is tied just put in park to help keep in place. I head of a lot of car coming lose in trailers this year and doing lots of damages I would think this would help I know they say it puts presure on park pin but it tie down it should not move that much. In your street car or truck you park on a big hill and it don't hurt them with that weight. What is real reason? THANKS