I agree with RichM that those are the best beaches. The one around LA have very limited parking even for cars. You of course always have the option to take a cab to Venice Beach or something. It is not truck friendly in most of the immediate LA area.
If going north, Pismo Beach has a couple of places you can get to the beach or close with a truck.
I haven't been out there since last year, but most is probably the same.
Have fun!
Davekc