Don't 5th come with batteries and a propane water heater?
I like my showers too.
I usually don't run my generator in a store parking lot, but will in a truck lot with everyone elses noise there. (my noise is better than their noise)
If you have slides, park so you're near the edge of the parking lot, have the slide over the grass or shrubbery - put out a slide where it's not in the way. We do this in the truck lots also. If we can't find such a position and have to park in parking space like the trucks, we'll leave them in - we're only there to sleep.
Bill