I'm a native speaker from upper-Austria and we say "im Urlaub"(in dem Urlaub) whenever we are on holiday somewhere. My excellent-grandmother and grandmother are the sole men and women I've ever listened to making use of "auf Urlaub". When we want to say "We're happening vacation", we use "Wir fahren https://knoxrxchm.wikicorrespondence.com/3580174/urlaub_am_bodensee_fundamentals_explained