Why cant you just buy/rent your parking lot and put your trailer there? Or put it on a side of the road, outside the city, on public land?
I think you can do that only on designated gipsy sites. But I have no idea how you can do that sure. As I've heard form some polish blokes and a fellow hungarian IT guy (who's doing contract jobs across the country) if you have a camper van or a caravan, using camping sites is cheap option.