I would stay around Discovery Bay/Bethel Island in the delta. There is a park there that is really inexpensive. I lived in San Jose for 3 years and I really wanted to live out there but the commute was murder.
https://deltabay.org This puts you really close to wine country
The problem you will find in the Bay Area is most parks are going almost solid long term monthly with waiting lists months long due to ridiculous housing prices that are forcing people out of homes and into RVs. The delta seems still not affected too much and anything north of Santa Rosa isn’t bad. There are couple parks in Santa Cruz that are still not doing monthly people and staying daily/weekly.