Where to leave trailer for a day while traveling

I've had some nice campsite owners let me park it out in an unused field after check-out time so I could go see the city. At another place, I was taking a bus tour, and the bus company called a hotel that they do a lot of business with, and the hotel let me park it out back. In that case, they had some incentive to do this, as we wouldn't have been able to take the tour ($$$)