I’m in the Bay Area, and I store my Airstream under the “covered” storage area of a commercial lot. Between the roof of the storage facility, the west wall, and the large MH on my southern exposure, I’m pretty much in the shade all the time. By the time the setting sun sneaks through the gap between the top of the west wall and the roof of the structure, it’s very late in the day, and the sun seems to have lost its punch. I believe protecting it from the elements has paid dividends, as my Airstream is nearly 12 years old, and still looks new. Still, it does get dirty in storage, so I wash it at home or in campgrounds that allow washing. Fully enclosed storage would be very nice, especially if it had power, but when I first picked the spot I did, I couldn’t find fully-enclosed storage in a convenient location at an acceptable price. I’m sure you’ve found that Bay Area storage can be pricey. I spent a fair amount of time evaluating several alternative structures in my side yard, but could never fully satisfy myself relative to the aesthetics. Although I could easily hide the sides with trees, it’s difficult to disguise the front, though I tried. I also considered purchasing a small warehouse property, but dismissed that as well in favor of the covered lot where I’ve kept my Airstream for about 10 years. It’s in a location that is very convenient to 90+% of the destinations we travel.
Like probably everywhere, sun is your worst enemy. I wax with Walbernize twice a year. I haven’t found the salt air to be an issue during general storage, though we store in the East Bay, so I suspect the atmosphere is less an issue than along the coast. When we travel to the coast, CA, OR, or WA, I make a point of washing thoroughly when I get home. So far, we’ve had no problems with vermin, other than occasional ants. I keep a couple of “Grants Ants” in the rig, and if an infestation occurs, the storage facility takes appropriate action. I don’t recommend using a RV cover as the wind invariably causes enough fabric movement to cause physical damage to the coach within a few hours. I learned that the hard way on a prior RV, even though I had it tightly wrapped, with boards on top.
I hope this helps.