Sam's Club, Walmart, Home Depot, 24 hr fast food in large lots, truck stop diesel stations, large shopping center lots, and many more. do it all the time. see others do it as well.
i stay mostly in Sam's lots for 7-10 days at a time. some truck noise throughout the night, but otherwise has been safe.
even though there is an "official" no-overnite-stay ordinance in just about every jurisdiction of the country...i have not yet been approached by anyone.
my challenge isnt where to stay, but rather finding places to dump and get water for a few dollars or less.
i use this site all the time...
United States of America RV Dump Stations
and i try to call first to confirm availability.