Hands down, one of the best places to take an Airstream in the SF Bay Area is Santa Cruz Redwoods RV Resort. There's nothing quite like living among some ancient giant trees to make you forget about city life. These breathtaking redwoods emanate a special energy that you really can't feel anywhere else. Yet, you don't have to drive hours into the forest to get away. This park is a quick 35 minute drive from the Elite RV shop (and thus also a perfect place for those who want to get their Airstream rental delivered to a camp site).
The park is owned and operated by the nicest people, and their staff are super friendly. When we got there, they saw that our site was partially flooded so they immediately moved us to a dry primo spot (we didn't even have to ask!). Here's a map of their camp sites. Just a tip: we stayed at campsite 20 and loved it. I think campsites 1-22 are some of the best since the back of your RV faces the river, so there's some views and some privacy. This is one RV resort that definitely doesn't feel like just another parking lot. Also you can rent a fire pit for $5 (you can also bring your own as long as there's no cut-outs on the sides) and buy a bundle of wood for $7 to get the complete camping experience. And they dump out the ashes for you. If you're going to be there with a big group, you can rent out the clubhouse for a large dinner, and it comes complete with full kitchen and recreation room. And coming this summer the park plans to do some wine tasting events and breakfasts on the weekends.
One of the best things about this park is that it's right next door to Henry Cowell State Park, with its 30 miles of hiking trails. Check out that link for a comprehensive list of hikes categorized by difficulty and how much time you have.
Some other awesome places to check out while you're there:
Mount Hermon Adventures: a jungle gym up in the trees (but definitely not for those who are afraid of heights).
The Mystery Spot: A little touristy perhaps, but also just a fun place to see at least once for yourself. And get one of those bumper stickers that seem to be on every other car in Northern California.
The Santa Cruz Beach Boardwalk: a family fun institution since 1907, but now with modern rides for thrill seekers. And for the laid back types, there's always the beach.
Roaring Camp Railroads: for kids of all ages who love trains (but just come prepared with water and some of your own snacks since refreshments seem to be lacking here).
Santa Cruz Wharf: A great place to dine on some local seafood and shop for souvenirs. Also if you walk to the end of the pier and look down, you might see some sunbathing sea lions hanging around.
Natural Bridges State Park: Named after the limestone natural bridge, this state park is a beautiful place to take some breathtaking photos on the beach. There is also a Monarch Grove, where 100,000 butterflies roost in the eucalyptus trees from fall to early winter.
If you only have a weekend to spare for some much needed R&R then I highly recommend Santa Cruz Redwoods RV Resort. Even though it's less than an hour away, it feels like another world. And if you happen to have more than a weekend, then a perfect Airstream trip itinerary would be several days at Santa Cruz Redwoods RV Resort and then hitching up and towing to Costanoa for several days near the California coastline. This way, you can enjoy both the redwood forests of California along with its beaches. You get the best of what California has to offer but there's minimal driving time!