In Parking Lots
Get permission first
It's amazing that many Wal-Marts, Cabelas, and Cracker Barrels allow RV's to stay in their parking lots overnight. But you have to call ahead and get permission first. Don't rely on apps or hearsay on the internet, either. Pick up that phone and (gasp!) talk to a real person. Sometimes it's not even that the business doesn't want you there - many cities are passing ordinances against this, and you might get a knock at your door from the local police at 2am asking you to leave. Always clear your stay with the store manager first!
One night only
This should be obvious, but unfortunately it’s not. These businesses are allowing you to stop over on your way to your next destination. Do not set up camp here! Don’t pull out your camp chairs and grills. It's not a tailgate party, people! Leave those for football season. Arrive late and leave early. Don't take up their valuable parking spaces for their customers.
Buy something
These are businesses, and you staying in their parking lot costs them money. It’s common courtesy to go in and buy something while you're there. Make it worth their while. Let them know you appreciate that they are offering their parking lot to travelers for the night by spending some cash at their store and even saying thank you.
No dumping
Don't dump gray or black water in someone's parking lot! This should also be obvious, but we’ve seen people washing their dishes outside of their RV and leaving their leftover noodles on the ground. I'm serious. Like, what the heck? Treat their space like you would your own, and leave it better than you found it.
Keep it down
Seriously folks. It’s one night. There should be no need to pull out your noisy generators in a parking lot with other travelers who are tired from their drive and just want to get some sleep. Often the area set aside for RV's is small and everyone is close to each other so keep it quiet and be respectful.
On Slides and Stabilizers
There's a common refrain out there that you should never put your stabilizers down, disconnect your tow vehicle, or extend your slides while in a parking lot. While we get what they're saying, it's not always realistic. We have 6 people in a vintage trailer. We have to put stabilizers down for the safety of our frame. Many newer RV's with slides aren't even usable when they're in. And sometimes you genuinely need to run an errand to somewhere else in town. Use common sense, and try to stay on the down low!