There have been posts regarding boxes.
I ended up buying a hitch haul platform (with a fold up adapter that lets it fold up when not in use)and a Stowaway box that also fits into the 2" hitch on my 235S. Depending on the need I go back and forth.
I had found a product that mounts to the back wall of the motorhome with L shaped brackets but it is not available in the US. It was made by Omnistor and called CarryAll.
On a previous post someone had installed one of the diamond finished steel boxes across the length of what looked like a hitch haul platform. That mesage also has a link to a picture. It is in this thread. Somewhere around page 15 I think I remember.