You need to check with your local council, they may have a byelaw preventing such parking, but if they do not, the highway code says the following: Cars, goods vehicles not exceeding 1525kg unladen, invalid carriages and motorcycles may be parked without lights on a road (or lay-by) with a speed limit of 30 mph or less if they are
at least 10 metres (32 feet) away from any junction, close to the kerb and facing in the direction of the traffic flow
in a recognised parking place or lay-by. Other vehicles and trailers, and all vehicles with projecting loads, MUST NOT be left on a road at night without lights.
Law RVLR reg 24
As the caravan is a trailer, as it is not self propelled, then it MUST have lights illuminated at night, wherever it is parked.