I have a permanent location, but I am only open 13 nights a year. I am required to have a special events permit which is issued by my county's building codes enforcement division. In order to obtain the permit and open my haunt, I have to pass building, fire and electrical inspections each year. In some jurisdictions you may be required to obtain a certificate of occupancy vs. a special events permit. As you mention, requirements vary by jurisdiction. Contact your local building codes enforcement division and make sure you have all of your bases covered before opening. Nothing worse than being shut down! You will also need liability insurance for your event.