Where can I sleep overnight in an RV nearest to SFO?

You may want to revisit your Walmart plan

And get out into the country more.

The US is not uniformly covered with Walmarts suitable for overnight RVing. Your use is tourism, but it strongly resembles "locals living in their vehicle", aka #VanLife, which is widely equated to vagrancy in urban areas.

Thinking particularly of the Bay Area proper... many local jurisdictions are acutely aware of #VanLife and actively combat it. This is because affordable housing is such a problem there and #VanLifers there number in the tens of thousands. Zoning may not allow the Walmart (or any store in the mall) to be open 24x7. Malls often have agreements with police to allow police patrol in the malls, who are on the lookout for #VanLife'rs. Streetside parking is also likely to get the 2am rap on the door.

Everything changes once you get over Altamont or Pacheco Pass or out into the Sacramento River Delta. From the airport this is a 1.5 to 4 hour cruise depending on traffic. Now it feels like the "normal" America they're talking about with that "park in the Walmart parking lot to sleep" advice.

Travel centers

"sleep in travel center/truck stop parking lots" works because I am talking about the sprawling 20,000++ square metre facilities such as these brands: Petro, Pilot, Love's, Flying J, etc. They have separate parking areas and fuel pumps for trucks and cars. These types of places do not exist in the urban areas where "no sleeping in vehicles" is enforced.

There is a Petro:2 on Pacheco Pass, and a bunch of stuff in Tracy. I wouldn't be any closer than that.

if you're in the kind of rural territory that has truck stops, parking to sleep in Walmart parking lots is almost always OK, provided they are open 24 hours, which most are. As far as shopping, though, Target is quite a bit finer, cleaner and generally more upscale.

Don't even try to park an RV in San Francisco

Herb Caen stylistically referred to San Francisco as "the City". Don't even think of trying to park an RV anywhere they capitalize City. NYC, City of London... Just nope.

Yes, there are secret places such as way out on the avenues along Lincoln... But do you really want to spend an hour on Muni transiting back to your Airbnb?

Plan to return the RV before your City stay.

I agree with Harper that Walmarts don't universally allow overnight parking. One of the best resources is the Walmart RVing Yahoo group. They take reports from people on the road and keep a comprehensive list of which Walmarts allow overnight parking vs. those who do not allow it.

The keeper of that list is Bill Halberstadt: http://halberstadt.macmate.me/Walmart/Walmarts.html

Note, it looks like this website is having issues- the direct links to the files are: PDF: http://halberstadt.macmate.me/Walmart/Walmarts_files/Walmart%20Parking%2010_9_16.pdf Excel: http://halberstadt.macmate.me/Walmart/Walmarts_files/Walmart%20Parking%2010_9_16.xls

And then there are overlays for mapping programs.

Otherwise, for smart-phone/app users, the AllStays Camp & RV app is very useful BUT it's $10. The free RVParky app is good (but not as good as Allstays).

For San Francisco, you might be best off just renting a spot at a RV park. It's expensive, but it gives you a place that you can even safely leave the RV for the night. I recently stayed at the San Francisco RV Resort. It's a parking lot (literally) and super snug- but for touring SF, it was a fantastic location. I'd go back again.