Saw out the outline of the paddle in 3/4" plywood, oak, maple, hickory, or other tough wood. Make a lever that the user will use to pull the luggage scale with. Then drill the holes. Cut out the center tongue as shown at right. I used a band saw for the two long cuts down the tongue then used a jigsaw to join the two cuts. Sand and finish with a tough marine varnish.
A note on drilling the holes: the mending plates on the bottom share some of the same holes as the corner braces on the top. I could see no way around it. You just need to be precise in your drilling.