The docks have great and secure parking by valets. I suggest you use that.
Holiday Inn does a park and stay package.
Have you thought of going by coach,we use Evesway coaches if your near a handy pick up point,they get you right to the ship and back to your pick up no stress no carting luggage,try there web site see if it compares in price?
Wre have recently stayed at Elizabeth house hotel. It was excellent value for money, clean, good breakfast and friendly staff. We parked our car there for the duration of our cruise. We have booked again for next year.