Signs all over saying that there is no overnight parking. We ended up staying at Sam’s club which is the next parking lot over.

Don't worry about what the other guy said, the manager puts up no camping signs so they can more easily remove people who are abusing their generosity. You want to park in the south east portion of the lot near the horse pens, which is between Cabela's and the Sam's club side. I have been parking here for years as I cross through Montana, it is one of my most dependable spots and it is appreciated. As long as you respect the space no one will bother you. During the travel season there will be several RVs here