Several people have mentioned parking at WalMart and KMart lots, with contrary opinions on whether this is okay. In my area there are also still a few Target stores that might be candidates, and other large venues exist in almost any US area.

Whether or not overnight parking is permitted is a decision made by the individual store management, often reflecting local ordinances. A few of the "Truckers Map Books" attempt to list places of this kind where it's permitted for trucks and presumedly would be permissible for other travelers. There also are web sites (sometimes well hidden from the "civilian" population) where lists of this sort can be found. Unfortunately, frequent changes in store policies make it impossible to place too much confidence in these listings, so it's usually necessary also to ask on arrival.

It must be noted that the "person in charge" when you arrive and ask is unlikely to know what the actual policy for his/her store is, and/or may just be in a bad mood when you get there, so you must be prepared to "be persuasive."

"Self-standing" places like the above mentioned are usually more likely to be agreeable. Large malls with many shops often have "mall rules" (and regular prowling security) that prohibit overnighting, or - despite their large empty lots - even temporary parking of "oversize" vehicles; and individual store operators probably can't give you permission.

Rest stops on US Interstate highways are "iffy." Each state generally has different rules. Several states post "no overnight" parking, but you can sometimes get by with 6 or 8 hours of "taking a break." Others posted the same way may "move you along" if they suspect anyone's asleep (an insane and inane rule, IMO). In many states you may see "Parking Areas" that are a bit different than "Rest Areas." The Parking Areas have no facilities, and are intended primarily for truckers who are required to stop and sleep for specified periods. Some states/localities will permit vehicles without ICC registration to park in them and some will not. (And the reefers on those trucks will keep you awake anyway.)

Oklahoma recently had all Interstate rest stops closed for about 5 years, because some local fundies decided that the lot lizards were having too much fun in them. Most of them have re-opened, apparently about a year or so ago. Kansas has had an isolated few rest stops closed for the same reason; but so far as I know they're all open now - except for the seeming 30 - 40% that are in construction zones.

Municipal ordinances, and the personal bias of local enforcers, may largely determine whether you can park at places like schools and/or churches. In my area, even the grade school lots are inadequate for staff parking, and high school lots are overstuffed since kids who live 3 blocks away all seem to feel the need to drive.

And in most states nearby my area, all Federal, State, County, and Local parks have "per vehicle fees," some have "per person fees, and many have additional "camping fees," so finding a freeby can be a challenge.

John