First you want a flat surface for the keel tray. Should you goof and the keel is on the wing, the weight of the boat will either bend or break off a wing.
You need to provide photos of the trailer for better responses as I asked you to do. Please provide them. I was involved in designing sailboat trailers.
The owners manual does not have the width of the wing keel. Unless one is on the hard or stored in a yard to measure the width, the only choice you have is to call Mars Metals located in Canada who extruded that keel
Please provide the requested photos