I finally bought a new generator. I chose the SDMO 2kw suitcase model shown below. It was only £550, which for a generator of it’s power is quite a decent price. The nearest to it was the Honda 2kw which was over £1,500.
It uses the same engine as the Honda, and since trying it I’ve found it lasts about 11-12 hours on one tank of petrol which is about 7 litres, which is phenomenal. It’s not quite as quiet as the Honda, but it’s quiet enough that if you’re in a noisy place, or 30 feet from anyone it will just sound like an engine running.
Running the van engine was very costly in diesel, and I was told that HDI engines weren’t designed to idle for long, so running it for hours to charge the batteries was going to damage the engine eventually. So far I’m very happy with it and it’s going to save me some cash too.