Highly recommend you pick the car first and park it in the car park at the ferry terminal. It looks a wastage of early picking up the car and just park it. However, I did have the same feel as you last x’mas. I went to the terminal by taxi and took taxi to Avis to pick the car in next day. Total taxi fee was more than I extend one more day on car rental. Also, it is also more flexible and convenient if you can drive to GC right away from the terminal.