Staying in a charger spot for longer than you need to, even if they are empty, really isn't great etiquette.
Since it looks as if the Mt Shasta Supercharger is located at a Best Western, maybe just pull to another space at the hotel. Otherwise I would have suggested a hotel or Walmart parking lot (they generally invite campers to stay overnight, and they monitor parking lots often)
Or, of course, get a room and have a nice shower!
Oh I would definitely not occupy a charging spot all night. I would park in an empty non-charging spot (there are hundreds of them at the Shasta mini-mall attached to the superchargers) and then in the morning plug in my car for a few min and take off.