I used to live in that area and I can honestly say that I'm not familiar with any regular RV camp parks close to SF. I guess I had no reason to know at that time in history either but no matter, I believe that there is something on the north side of the Golden Gate and maybe even something in the Presidio. Google may be your best bet here.
But if anything, I'd highly advise NOT trying to pull a large trailer anywhere near the heart of SF. Traffic can be terrible, very congested, and people have zero patience around there. I've seen small RV's in the city and I think those people are crazy since finding parking would be next to impossible.....and very expensive. If you must pass through then stay on the major freeways to get to your destination, but just make sure you know exactly where you're going because there's lots of junctions as the 280/101/1 are close together, lots of turn offs, and trying to get off to turn around would be very difficult.
Its an amazing city if you know where to go. Having been there many many times, tourist points are fun but the real fun is knowing where the non-tourist spots are.