Although I do use park when transporting, I also lock the hand brake and lock the vehicle with so many HD straps it can't move in any direction even if I roll the truck. With that said, the reason they don't want you to use park is that the "parking paw" and slot are not designed to take jolts back and forth..like dropping it in park while moving.. and can bend the arm or break the paw. If no force is or can be applied to it through the transmission from any kind of movement, then it's OK. But if there is any chance that by driving rough roads or hitting the brakes hard you would put extra load on it, leave it in neutral cause ...it will break it...and has several times to others. In fact...the more I think about it..I now will stop using park during transporting just to be 100% safe.