I did a test with the C10 towing an empty trailer weighing about 180 kg, so nothing particularly heavy.
On the motorway, keeping an average speed of around 110 km/h, the battery dropped from 45% to 1% over about 95 km. I expected higher consumption compared to normal driving, but the drop was still quite noticeable.
In my opinion, the trailer makes a significant difference even when empty, mainly due to aerodynamics and speed. For long journeys it’s worth planning stops with plenty of margin, because with these figures I wouldn’t fancy pushing the remaining range too far.