Don't save the camper van for better times, for there are no better times than now.
Now is when you want to go, now is this minute, tomorrow, next week or next year. A Cali is all about now. Now is when you look at the weather forecast, see strong winds and gales, sunny in parts and go to parts that are sunny. Or crap winter weather all over so lets go to a theme park, stately home or Portugal.
Give in. February is a rubbish month. Leave it until accuweather gives you a week's forecast and go where it says "nice for a week" or "less crap than anywhere else for a week".
Seriously, a Cali is something to keep packed, charged up, fuelled up, ready for when you say "let's just do it".
If it was me then I would head north. and as you are already half way up north then go further North. If it's going to be a really rubbish winter week then go where the rubbish weather translates into spectacular weather. Warm sleeping bags, on board heating, decent boots, good coats and enjoy what nature can deliver in our worst months. London might be warmer but hey, if it's a choice between clear minus ten, wet zero or damp plus ten then give me minus ten every time.