City right-of-way: permit needed for holiday market porta potties?

I'm organizing a holiday market in our downtown area this December and need to place portable toilets on the sidewalk. The event will run for three weekends, about 8 hours each day, with an expected attendance of 300 people per day. We'll have food vendors and serve alcohol. I'm planning for a mix of standard units and at least one ADA-compliant unit, all on level concrete. The spot is near the curb, so a vacuum truck should have no trouble reaching it for service. I know cities often require permits for right-of-way placement, but I'm not sure what the process involves here. Do I need a special permit from the city for this, and are there specific rules about how close the units can be to the street or crosswalks?