I reserved at Port of Miami Parking http://www.portofmiamicruiseparking.com
It's 2 blocks from the port. $6 a day and a $5 a person one way shuttle. It is not 24/7 security, but it is fenced in. I'll be leaving nothing in the car for anyone to take and I have full coverage.
They suggest dropping off your bags at the port then going out to park. As long as we don't have any last minute shopping to do I might drop off bags and Steve at the port and park by myself. Save the $5 shuttle for him. Getting off the boat we will play it by ear. If the cab line is short we might jump in it. If it's long we might call the shuttle. If someone leaving will drop me at the lot I can leave bags with Steve and come right back with my car.