Shower facilities for Westfalia = Black bucket with hose and garden watering end.
Most campgrounds and parks offer showers as do bigger truck stops. YMCA's and a lot of other places where you can shower, shave, and get cleaned up. A river or lake works also.
Yeah, the Westies are definitely a West Coast cult thing. My Mom owned one and used to cover a lot of miles with a traveling partner so I know it can be done. Good choice on getting something smallish and usable if living in SF. That was why I initially recommended a truck and camper.
Good luck and have fun in your Westy.
