I just completed a 3000 km road trip with 4 bikes, for the most part on motorways. Two bikes on the towbar, and two on the roof. Trying to keep the speed at around 110-120 km/h on average, I ended up with between 230 and 280 wh/km on a 2021 model 3 long range. When it got windy that figure quickly rose to well above 300 wh/km on certain legs, but that wasn't the average.
Anyway, I had to do a lot of charging. I did feel the range was a little to short with this setup, which is something I haven't really thought about earlier.
Hope this helps.