We have been RVing for 10 years and full timing for 7 years. Have never stayed in a Walmart parking lot. Do not plan to.
If we can not afford an RV park to rest up when traveling, then we will stay in one place and quit traveling. This is my opinion and how we roll.
We have traveled coast to coast and north to south so we have not stayed in one place much. But still we do not sleep on parking lots.
I am sure someone will have something to say about RV parks could be dangerous too but we do research and choose where we stay in advance of our travels.