In 2006 we stayed overnight in the Sam's Club parking lot in Anchorage, Ak. (twice in three weeks)
As soon as we entered the lot at the Wal-mart we were told by a roving guard that we could not park overnight there.
He instructed us to try the Fred Myers lot down the street. We drove to Fred Myers, did our shopping, and returned to park on the opposite side of the street from Wal-Mart along with 15+ RV's and several large trucks, in the Sam's Club lot.
I have also used the Sam's Club lot in South Charleston, WV.