As long as you can park your RV in a decent radius distance, like 30 miles, from the city..... then simply find a nice place to stay and drive in. Get a map and spend the day in SF sight seeing, paying outrageous prices for parking, eat good food, and drive back to your safe spot. No point in trying to get close enough to be in walking distance. If you dont have a tag vehicle or a way to drive there then take a bus and get a City Pass and use the SF muni systems (bus, trolly, cable cars, taxis, etc.) to get around. That in itself is a sight seeing adventure. Lots of diversity traveling on the muni systems. :B