I practiced making him stand on his own at a distance from me, which he's getting comfortable with, even when the neighbours are revving their snowmobiles.
At the trailer, I had him step in and back out several times like yesterday, and then I was able to get him to turn to face the door and stand still. I asked him for a few back steps and forward steps in the trailer, and then let him walk quietly out.
He did very well, and didn't attempt any Lipizzaner moves like two days ago! Tomorrow he may be ready for me to close the door.