Hoppes has oil in it and when the solvent base evaporates it leaves a thin layer of the oil behind to coat the metal.
Since you live in Southern California where the relative humidity is very low, compared to the rest of the country, you should be alright with your present regiment of cleaning. But humidity isn't all that counts, wide fluctuations in temperature can cause condenstation to form on relatively cooler surfaces. Metals tend to remain cooler in the morning and can gain a layer of condenstaion on them just like dew forming on the lawn in the morning.
Having spent a considerable number of years in California, I can say that if your regularly applying the Hoppes solvent then you shouldn't have too much to worry about. Unless you live in the mountains (like near Lake Arrowhead or Big Bear) where the temperatures and humidity can swing big time.
Another thing that's bad to do is to keep any firearms stored in an attic because there the temperatures vary tremendously between days and nights. (I'm not saying you do this but others might and this warning is for them to read.) Condensation will form quickly and the oil just rises on top of the moisture and starts the corrosion cycle on the now unprotected metal. (Remember oil floats on water!)
If your concerned about rust or infrequently apply Hoppes, then adding a thin coat of oil to the surface won't hurt. Its up to you.
Shooters Choice, Hoppes, and many other cleaning solvents have the oil added into the solvent. However, Sweet's 7.62 doesn't, and due to the high ammonia content tends to suck out any remaining oils from the micrscopic cracks in the metal. If you use this kind of solvent, be sure to coat the treated surfaces with oil, or corrosion will quicky follow and damage your firearms.