Okay let's start with being honest. A campervan is not as fuel efficient as a standard car! It is much heavier and less aerodynamic.
Our published fuel consumption guide of 12-14 litres per 100km is there to allow people to budget and plan for their trip. As stated it is guide only and is the average for an entire trip that includes both city and highway fuel consumption. We have found this range to be a good approximation.
What you can control:
Speed - Cruising over 100kph will dramatically increase fuel consumption, whilst cruising at 90kph will give you excellent fuel economy (for a campervan!)
What you can't control:
Wind - If driving into a headwind it greatly impacts on the fuel usage. As the camper has a high roof it is not aerodynamic and will use a lot more fuel.
Terrain - Driving over hills will increase fuel consumption as the engine is working much harder.
We highly recommend that you drive conservatively. This will give you the best fuel consumption. You are on holiday, take it easy. Please also be aware of vehicles behind you and pull over where safe to let faster vehicles pass you.