That's rubbish, off course.
Both vendors above quote about 250-300 km. Which is perhaps not as nice if you're dashing to the south of France (although: you would probably have to pause every 2-3 hours anyway, so why not load her up then?).
Anyone ever driven a T1 or T2 campervan? You would have to fill her up every 250-300 km's, which was about a day's drive as well! Not counting repairing the punctures etc. along the way. Those were the days!
We may just have to re-think what once was a nice campervan holiday. Not dashing 100's of km's and then stand on a hard standing pitch on some very expensive campsite in Italy for 3 weeks with our awnings and all, and then dash back. But rather leisurely cruising along winding back roads and see what we come across in terms of sights, nice coffee and lunch spots, etc. You wouldn't be doing more than 250-300 km a day. And that seems already very well possible with a nice ID.BUZZ camper.
Our € 0.02. We may move over to the dark side!