Finally finished my rack. Took some time getting the proper material but the wait was worth it. The original was made from a cutting board and had silver fleck and was smaller than I wanted. The new material is solid black and the blank was 12" x 18" which allowed for a larger rack. The material is commercial 7/16" black vinyl which is both durable and weather resistant. Used my hand saw, drill press with 3/4" and 1" spades bits to shape and drill the material. A simple task IMHO.
Bob - good looking platform. I did a similar board ; but mounted it on top of the small factory rack. By the way , I stood on the factory rack with all my 190 lbs. ;it didn't even try to break. I had to know before we left on our road trip. We strapped at least 30 lbs. on it for 3976 miles.