you're going to have a hard time finding anything near Irvine for that long.
especially for the time you want to be there. state park campgrounds in the area, are probably already reserved for those times.
we reserved some coastal sites for February and couldn't even get 5 days in a row anywhere.
i'd suggest a mobilehome park, for that length of time.
or you can go inland and probably find something. like Lake Elsinore.