Just this morning I finally made a couple of the patented B~C Centering Shoes for my trailer, and they worked great. It's just a carpeted chunk of 2x4 with an angle bracket on the back that slides down over the side guides. After the boat is on the trailer, and still deep enough in the water to move sideways, put one of these deals on each side and they hold the boat snugly between them while you pull it out. Then you take 'em off, and the boat is centered and the side guides are not even touching it.
I'll see if I can find the old picture that Ken posted and edit a link to it in here. Ken might play the part of an undereducated educator educated beyond his intelligence, but he is mighty crafty and a fine craftsman. And his centering deals are a stroke of genius.
By the way - my King for the CD25 has four boards. My CD22 trailer had rollers, so it doesn't count in this discussion.