I have my own set of rule, imposed by me, for parking at Wal Mart.
1. Its late and I've reached my driving limit for the day.
2. I don't need to run the portable Honda/ Champion, whatever brand generator for any reason.
3. I don't need to pull anything out of the travel trailer except my coffee mug and my carcass in the morning.
4. It's the day I start dry camping, the refrig has been finally turned on and chilled down all night, and I need to fill it up with groceries from Wal Mart.
That officially makes me a customer, not a mooch or free loader. I make a point of thanking the manager for the parking overnight while walking out with a few bags of groceries and things I need, usually a triple digit dollar purchase.
That makes me valuable to Wal Mart, and wanted as a patron.
YMMV, that is solely my code of conduct and ethics. By leaving money with them, and doing business with them, I make myself welcome and wanted as a patron. Even if my trailer does take up a bit of space in the process for a little longer than necessary to complete the transaction. Everyone goes away happy. Win win situation.