Well so much for that.
The port itself might accommodate you, but you would have to call them. They might be able to park your motorhome on-site, but not in a normal parking area. They can probably shuttle you to your cruise terminal if they can do it (they often shuttle people from alternate parking areas when the closest ones are full). But i'd expect it to be fairly expensive.
The only other option I can think of is using a service like Cruise Connection. They have commercial buses that pick up cruisers from the outlying cities (Tampa, Orlando, Daytona, and several other cities), then transport you to Port Everglades cruise port in Lauderdale.
Ft. Lauderdale & Miami | Cruise Connection by ESCOT Bus Lines
To use this service, you would have to find a storage lot for your RV that is near the pickup/drop-off location (usually a McDonalds or similar resturant). And the fare to the cruise port is not cheap - $100 or so per person.
One idea might be that you might find a RV park in one of these cities to stay for say a month or so that will allow you to either leave it there in storage or rent a spot for the duration of the cruise. Afterall, that is why you are taking your RV right? Then you would have to find local transportation to the pick up point; taxi, etc.
It's doable, but would take some planning.