The Bedford HA vans that my BT colleagues use to drive (not me, I was exchange-based), certainly had steel wings. Certainly, over the years they managed to put plenty of dents, dings and scrapes in them, and they certainly rusted! Maybe you were thinking of the early Morris Minor vans the Post Office (both Royal Mail and GPO Telephones) that used to have rubber wings (with the headlamps mounted on top) ?