Mike,
Being from the U.K., there's another related issue pertaining to boondocking that you might not know about. California and the other western states have a lot of forest fires and this year has been particularly bad because of the drought. Our firefighting resources have reached their limits and the fire season isn't over yet. If you're boondocking somewhere and accidentally start a fire - well, you just wouldn't want to do that. We call them "forest" fires, but really any area that has low-lying brush, even without trees, can have wildfires so "they" are really tough about not camping except in designated areas. Wildfires endanger lives and property which is why throwing a cigarette out a car window in California is illegal. If any in your group are smokers, please do us all a favor and alert them to be especially careful about extinguishing their smokes safely and properly. By the way, most national and state parks have signs that say camping is allowed only in designated areas. These days most are also prohibiting campfires and occasionally they close a park because the tinder is just too dangerous and they don't want to take a chance on having a fire burn out of control.
I agree with Tom. In driving along the coast on California's route 1, there really aren't many places to pull off except designated areas. There's lots of private property and, unlike in England, the public is not welcome to use trails across private land. We were quite amazed in England when our friends took us on a short hike where the trail took us across private property. Your land use laws are different in that respect. Carl's suggestion about the State Park beaches is a good one. They're in great settings. Also Tom mentioned that camping alongside the road usually is illegal. This applies to highway rest areas as well. You're allowed to stop for a brief rest, but most have signs prohibiting overnight camping in rest areas.
Boondocking in the U.S. often implies shopping center parking lots like Wal Mart. This company is RV friendly, but many communities are alarmed over the growing use - and abuse - of such boondocking sites. As a result they have enacted city ordinances prohibiting overnight camping except in established campgrounds. Be sure to look for signs indicating such ordinances. It's always a good idea to ask permission of the store manager and do some shopping there to help them continue to want RVers. The large RV organizations (Escapees, Family Motor Coach Assn.) have adopted an etiquette code for boondocking in an effort to stave off more anti-RV city codes. Most are common sense such as no waste tank dumping in parking lots (yes people do that and I actually saw it happen once), don't put out awnings and slides, no BBQs, lawn chairs, etc. In other words, don't set up a campsite. You are merely parking there and don't want to make it appear like you're there to camp.
While many of us were attracted to RVing because of the ability to have a "wilderness" experience, the fact is the world has changed and people are more touchy these days about protecting many things and places. Sad, but true. Even with these boondocking restrictions I think you'll enjoy your RVing experience here. They're not really as bad as it sounds.
ArdraF