damn...those are rare..
Not really.  One came with my '90 Westy, color was wrong, apparently
originally from a brown/beige interior instead of the gray interior on
my '90.  I was told these 'jump seats' were originally standard issue in
Europe, are for holding the chemical toilet that is required to be
licensed as a camper in Europe.  It was big an bulky, took up more room
than needed for my toilet, and I traded it off for some other items I
needed (like the jack that was missing from mine when I bought it).
I've seen at least two others since then.