I have one of these, except the Riviera version, not the Westy one. It's an ok idea, but makes moving between the front and back kind of a pain. It also slides around if you have a rubber mat (as opposed to a carpet) in the middle section as I do.
I have this exact Plaid Jump Stool in my 78 CE Westy. It's a storage Box as well as the Step Up Stool to the Top Bunk. It straps down to prevent sliding and can be easily removed if need be.
I've never seen Go Westy sell these, but as another reader stated...they can be found from time to time on E-Bay. The Exact Plaid Material for your interior can be found online through Go Westy -through another supplier I believe.