Here is what I would do for a one day fix.
Very very early in the morning launch your boat at the South Shores boat ramp located in Mission Bay right off of Sea World Drive.
Once you have done that (again, very very early) you then drive your motorhome a short distance to Fiesta Island and find yourself a good location to make your camp which can be right on the water. Then have someone bring the boat over to your beach front (actually bay front) location for the day, kickback BBQ and enjoy the fireworks, and it's all free.
Be prepaired for tons & tons of boat and people traffic and plan on staying put in that area till later in the night.
The unknown fisherman