San Francisco Bay Area if you please. The Bay Area if you must.
Check the Pleasanton Fair Grounds. Reservation will be necessary if they have space.
There are some mobile home parks that might work. Look East of Claton on Marsh Creek Road.
Lots in the Delta. Not too many where you specified.
If you are WBCCI check for courtesy parking.
I would probably stay in Rio Vista. Duck Island RV park. County across the water. Bandon Island State Park is a little closer. Reservations.
Also Flag City at I5 and 12. May have drop in space. Close to highway.
Good luck. Pat