The best solution for winterizing your RV is to use indoor storage. Out in mild California climates like Riverside, Corona, Lake Elsinore and other areas of Orange County and Riverside County, the winter doesn't pose as great a threat as other parts of the country, but regardless of where you live, indoor storage should be option one.
If you choose another storage arrangements, however, here are the key winterizing steps you should take:
1) In cold climes where temperatures routinely fall below zero, the first worry is water freezing. The only two solutions here are to drain the system completely, making sure you get out every last drop, or using an anti-freeze that will withstand the freeze. Inside water units can also be affected, and if you can't use anti-freeze on them, you'll have no choice but to drain everything inside (or choose indoor storage).
2) Using a tarp to cover the RV may make you feel you've protected your RV, but most tarps will trap moisture underneath them, creating mold and mildew. If you choose to use a tarp (and not indoor storage, for instance), find one that's breathable.
3) To keep moisture from forming inside the RV, try using a chemical absorbent or a heater.
4) If you choose not to use indoor storage and park your RV out in the elements, try to park it on a paved surface. There is no need to remove the tires; they'll survive fine. But if you park on mother earth, when the spring thaw comes, you may find your RV sinking into the soft ground.
5) Mice and other critters will seek shelter in and under your RV during the winter. Mice can easily squeeze through even the smallest of openings, getting inside your RV and chewing paper, curtains and other substances. There's really no way to stop them, and when it comes time to use your RV again, you'll have to spend long hours spying for animal infestation. (Indoor storage, anyone?)
6) Ants and insects are another threat, especially as the weather warms up. Some RV owners place moth balls or dryer sheets inside the vehicle to help control the migrating insects.
7) Propane in your RV's tanks contain an order that strangely attracts spiders. Many owners will remove the tanks for the winter and stow them away, but be sure to close tightly all piping and fittings supplying propane to the RV.
There you have some important tips for winterizing your RV, but again the safest, cleanest and least labor-intensive solution is indoor storage. You may still want to observe many of the above steps, but your RV will definitely be safe from nature--and from human nature (think vandals and robbers).