Got some drywall sandpaper, some thin wood the length of the
aforementioned block and about as wide or little wider than a rail, and a
couple of scrap brackets. I Sanded the edges and corner of each flat so
when finished it won't snag things while cleaning.
After painting, I wrapped the drywall saandpaper around each flat wood
piece and screwed then to the main block. They should be a little lower
than the main block, as they will be used to contact the rail
without hitting the flat crossing.