Good luck on your search.......
NOT much to be had close by.
Dockweiler RV Park........LA County Park on the beach But only 21 days per 60 day period and 60 days total per calender year.
Not sure about how safe....it's an isolated area (power plants, chevron oil facility and at end of LAX flight path)
Then there is Golden Shore RV park in Long Beach
But travel can be a PITA due to traffic up the 405 (roughly 22 miles which could be 25-30 minute drive or 2 hours)
Not cheap either
Welcome - Golden Shore RV Resort
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Doesn't LAX still have employee RV parking in one of the LOTS?