I'm from WA, so don't know Tas that well. Cradle is lovely, but it's often cloudy with unpredictable weather. I would guess east coast is best, weather wise. Maybe try the bay of fires? North east coast is optimal, because Gemini is a northern constellation, so further north will mean more meteors.
If you're on Facebook, follow the Tasmania Aurora group. They shoot night shots + aurora all over Tas with amazing results. You should also think aurora when you are down there.