We looked at hiring a car for the day, but decided to go with a private tour instead, it was more expensive but I'm really looking forward to having our own guide for the day! I contacted Tours around Tasmania who were able to help put together a tailored day out for us, I can't wait to see Hobart again! The Argyle Street car park in Hobart's CBD is probably the most secure, but also the most expensive. From memory it was about $25 for the whole day last time I was there, so not sure what their overnight fees are like!