KOA in Petaluma has good storage rates. I stored mine there for a month or two before we started full timing.
Boondocking is tough in the area.
There are some areas in SF that have looser parking restrictions than others, and you'll see the "urban dwellers" in their old motorhomes in the area that move once/week to avoid street sweeping tickets.
Couple spots I've seen them that are in good areas:
- Post St (btw Scott & Steiner) around the Hamilton Park
- Jackson Park/Playground. 17th & Carolina
I'm not sure if the rules are different for trailers, but I lived in SF for a number of years and saw the same RVs in this area time and time again.