In this post in the Van Life Q&A, a user asks:
Urban camping questions
I’m no expert but here are Some ideas that have worked for me in the van, my previous truck, and a huge shiny airstream trailer.
Hotel parking lots that are fairly full.
Light industrial or commercial office districts that have cars overnight that you can blend in with.
Truck stops and rest areas. If rest areas say no overnight, just roll in late and early. If you get woken up it’s fine, just tell them you’re traveling and tired so you need a nap to be safe to drive. Out of state plates help a lot with that.
Paid Parking garages if you can fit in and the rates are OK.
While it’s noisy, anywhere you see semi trucks overnighting is usually ok too.