Hello edfos2 -- I am looking at a NY Times book (Times Books) from 1984. This references areas all over the world. The NY Times combined all of their daily weather reports over the years into a month by month record of average temps, record hi & lo temps & precip. Of course they only have San Francisco in the book. But they do record the lowest San Fran temps as 28, 28 & 31 for Jan, Feb & March. Are yours a few degrees lower probably?
I realize you are a bit SW of San Jose and maybe you can tell us if your experience is different than I mention above. This thread
is one example of the west's Leipper
having actually recorded temps inside his trailer in temps that dipped briefly below freezing. Another more recent thread of his actually reported colder temps in which the interior temp didn't get very cold. Now this advice won't let you travel to higher elevations with impunity but I'd expect that you wouldn't have to winterize at all at your elevation. That is assuming you don't have an outside shower -- which shouldn't be the case with your year.