In my 44 years of traveling around the USA I have never had staying at a Wal-Mart or any other parking lot as my only option and it will always be the very last place other than an active landfill dump where I would choose to spend the night.
There are zero advantages to staying at a public parking lot and I always know in advance where I am going to be the following day and what my options are for spending the night. If I can make it to a city where there is a Wal-Mart than I can make it to any one of a hundred places in the area where I can stop and sleep.
There is a misguided herd mentality that drives people to think that Wal-Mart is the only free place to safely spend the night with an RV when nothing could be further from reality.