We probably don't get away as much in the winter as most on here as we have two young kids in school but my summer figure is spot on. We've headed to France the last three summers for about 3-4 weeks each time, filled before we left and only used about a third of a tank for the trip.
Using the gas for toast and tea in the morning, some hot lunches, dinners most days and multiple kettles of tea throughout the day. Along with heating the water for the above wash ups and showers too. Have done multiple week trips to Wales at Easter too with similar loads using the heater too.
We do have a small compressor fridge which runs off the solar so don't use the gas for that. The van is a 6m well insulated Ducato panel van conversion with a big 1m tall by double bed size garage for bikes and gear at the back so the space inside to be heated probably isn't massive either.