Employee lots probably have restrictions on camping, too much drama, especially when some folks make it their full-time home.

LAX used to have a lot dedicated for crashpad campers, but they shut that down a few years ago. I know you can't camp in the regular lots.

I assume they won't let you park a large RV camper. You might get away with a sprinter van or the like, but you'd probably have to be very low observable and play keystone cops with the security guards.

I don't know about ORD, but probably similar.