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This bus will take you from LAX to Santa Barbara there and back - they have lots of time slots throughout the day.
I would recommend Enterprise, you can easily pick up and drop off at the airport - but there are a lot of good companies! Having a car will allow you to easily travel around, as California doesn’t have great public transportation.
The train is a bit expensive, but can take you to and from various cities along the coast.
RV Swap can be a really good really good resource - especially if you are planning on visiting multiple locations throughout California. You book your campsite, and the RV owner will drop off the RV at your campsite. Very convenient if you don’t want to drive with an RV, everything will be set up for you.
Outdoorsy seems like a good place to get RV rentals all over California