Parking at San Diego is so easy, googling can find you lots of options, all very close. Even airport parking offers shuttles to the port. Prepaid gets you the cheapest option. Like Peachypie said, we have used Wyndham and they do book up, so doing prepaid in at least a month or 2 in advance will assure you a space. It is an easy walk across a big street ( you will need to cart your own luggage) When you return, you will need to show your prepaid voucher and your parking ticket to the Hotel bell staff to get it validated to exit.