Check the search function on Fulltiming. I've just celebrated my 2nd year as a fulltimer and I got queasy when I had to fly to Dallas and spend two nights in a hotel room. Those square walls and flat ceilings are creepy! Plus I know whose DNA is on what surfaces inside my Airstream Hotels?...eeeewh!
I respect and admire vintage owners who do the "full monte" and restore older Airstreams. But I don't have the energy, the place, the time or the drive to do it myself. If you're working full time and are looking for an "affordable, portable apartment with equity" look for something 3-5 years old.
If buying new is out of the question, be aware that buying a close to new one can be quite economical, and buying brand new can allow you to finance it. (You do take a hit on the first year depreciation).
For starters, look in the classifieds here. New Mexico and Arizona are also the "happy hunting grounds" for used Airstreams. They stay well preserved in the dry climate and many are used only in winter by snowbirds. Sooner or later health fails and the Airstream, often fairly new, must be sold.
Good luck, Sorry I can't advise about parking in the San Diego area - but give us more details on where you'll be working or stationed and I'm sure someone from the area will chime in.