Many will gag at this, but Dockweiler RV Park (I think it's a county park) is the only RV park on the beach between Point Mugu and San Clemente. It's great if you want to be in the city, on the beach, on the bike path, and can stand a little noise (on the weekends) from party nuts. Reservations are sometimes hard to get on the weekends, but my experience doesn't cover the winter (is there winter in L.A.?).
Dockweiler is just a few inches south of the LAX extended runway centerline, but the airplane noise is really not noticeable and they quit flying around 10 PM, anyway (no lifties in late night air, I guess).