Places to camp or layover in Orange County are uncommon. I would go so far to even say the L.A. basin is the least RV friendly metro area in the lower 48; well, maybe NYC is worse but there are places there too to overnight. Of all the 'made for living in' RV's that have the smallest footprint, a hard side truck camper fits the bill. Why? It doesn't change shape and does not look particularly like you are on vacation. With the shades drawn, lights off, I does not look like anyone is home. This is with a range top, 2 sinks, a small fridge, hot water, a furnace, a toilet and 2 showers, 200Watts of solar, LED lighting, a queen size bed that we get the best night's sleep ever. Some of the appliances are 3-way: 12vDC; 110vAC; propane. We have successfully camped/overnighted down to 05 degrees F and lived to tell about it. Don't try that in an all metal Van with no insulation. Jeanie and I have spent more than 200 nights, many of them stealth camping (I prefer, "layovering") in cities, large and small. In our case, we are really traveling and just having a layover for one night. There is an art to finding a good spot for the night. The thing is, one night is enough to not draw much attention to yourself. Spend a little time exploring Tioga George's Blog. He spent 25 years in a Class C and never paid for lodging. Another good bet is to go to RV.net/truck camper forum and search full-time or long stay or part time. There are surprisingly a lot of people out there that have done what you want to do and learned the ropes.
How about exploring the campgrounds up Trabucco or Majeska Canyons? Many Marina parking lots allow boaters to overnight near their boats. This place you're going to do some work for: do they have a back lot you could conceal yourself in? Or, any connections to a storage lot or similar.
When I was 6 months from retiring from the L.A.Philharmonic, we sold our home and moved to the West Slope, Northern Sierra Nevada, but I had to finish out my contract at the Hollywood Bowl. I tried to get the Bowl management to let me park my truck camper in the dirt on the upper storage area and run an AC cord to the warehouse, but it did not work out. Then I contacted a campground in the Valley to see if I could get a campsite for 4 months. The lady asked what kind of 'Coach' I had and I murmured that it was a truck camper. She said we only allow 'coaches' (code for big F-ing MoHo) and they must be less than 10 years old. That let me out even though my Lance was only 8 yrs. old. I was about to ask if I could park in our old Church's parking lot during the week when I asked a buddie who lived next door to the church if he could take me in for 4 months. He could and he did. I paid for room and board. It worked out great. Maybe the business could hook you up with an extended stay motel close by? There has got to be a congenial end to your search for living accommodations for specified period of time. Good luck and do report how you're doing. It would be instructive for many of us readers.
jefe