I thought that I would need guide-ons for the trailer, as there is no "V" for the boat to slip into with the flat bunks. I purchased a set of bunk guide-ons from Cabela's on sale. You start by mounting the support arm's clamps to your trailer's frame.

Insert the support arms into the clamps. Snug things up a bit, but make sure you can still move the arms in or out.

Attach the extender brackets to the bunks.

Last, attach the bunks to the support arms. There will be a bit of trial and error here to get the bunks at the right distance from the hull as you tighten up the clamps. For me, the guide-ons stuck out too far to be able to get the trailer out of my backyard. I had to mount the support arms inside the extender brackets with some extra washers. I narrowed the setup 4-inches this way, which was just the amount needed!

So do these things work? Well, kind of. They definitely let you know where the end of your trailer is when it is in the water. If you are the kind of boater that cranks his boat up onto the trailer, they will be indispensible. But my boat does not have a bow eye to attach to.

When I first started retrieving my boat, I was putting my trailer too far into the water. I kind of wanted to float up to the winch, attach to my anchor cleat, and pull the boat and trailer out together. Except that the boat would never settle in the right place on the trailer. Apparently the bunk guide-ons flex a bit. Now what I do is put the trailer half way into the water, less than what I did to launch the boat. I then start my boat's engine, and get the boat going about three miles per hour in line with the trailer. When the bow contacts the center bunk board, I simply power my way up to the front of the trailer.
Boat on!