Hey hey.   
My city by the bay.  I speak of travels from north of the golden gate in Marin county. I used to park my alfa romeo gtv at the corte madera larkspur  ferry terminal and commute into the city via ferry past san quentin and Alcatraz with panoramic views of the golden gate and sf bay. It is cheap boat ride and quite scenic. You can probably park at the terminal with your camper. 
Also try tiburon ferry on Tiburon peninsula. 
This will get you to the ferry building and market st. In sf. From there you can walk to catch the cable cars and travel throughout for cheap.  

Cheers
Joel

Sent from my iPhone

On Dec 21, 2012, at 10:59 AM, Doug Alcock <doug.alcock@GMAIL.COM> wrote:

> Hi gang --- while we still have our beloved 84 Westy BlueBelle we are
> currently travelling in a 23 ft Europa motorhome. We want to look around
> the San Francisco Bay area for a couple of days starting around Jan 10. In
> other cities we've been able to park somewhere (for free) and take transit
> around the city to sightsee without having to worry about driving and
> parking the RV. However the Bay Area Walmarts are not RV friendly and the
> local campgrounds are ridiculously pricey. Can anyone  suggest a place we
> can park the little RV for the day -- transit around town --- and return to
> sleep at night. We figure a couple or three days should do the trick. Also
> any suggestions of 'must see' things we should do when in the Bay area
> would be appreciated.
> 
> Thanks,
> Doug
> Mississauga Ontario
> 
> --
> http://www.dougalcock.com