I would agree with spending time in San Diego Harbor. The Chula Vista Marina is down South part of the Bay, but has an RV park, and ramp--should be warmest you will find in S. Calif--and maybe the cheapest.
In the Los Angeles/Long Beach area, I recommend Sunset Aquetic Harbor--Huntington Harbor ramp and marina. Nice houses on the water. I could afford one of these 40 years ago....There is probably the best on the water display of decorations during the Christmas Season in Huntington Harbor. The parade is not to be missed. Also Newport Bay has great decorations and boat parade. More pricey at Newport. If you think the "Dunes" in Monetray is expensive--Newport may be more...
A trip to Catalina would be nice--both Avalon and the Isthums this time of the year. However, it can be cold in S. Calif, and windy. Do your crossing before 10 AM to avoid chop and wind. Although you may find 70's in this area--there is dense fog predicted for tomorrow AM...and Rain the week of Dec 1, with some lower temps.
Also be very aware of "Santa Ana" winds, which are catabatic winds, and can reach velocities of 90 knots off shore....can be very dangerous for small boats.
There is usually good warning. But this is the time of the year.
Have fun in my stomping grounds of many years!