Fuel tanks being exposed is generally a bad thing, and we generally tuck them away from the hazards that would damage them.
To allow access there are fuel lines leading into the tanks from the exterior of vehicles.
I propose an element that achieves this same function in Dual Universe. It could be linked to a tank (possibly several) to allow for one way fueling to the connected tanks. it wouldn't make the tanks capacities shared in use with other elements, but would allow for them to be internalized in the vehicle protecting them better from outside complications.
The logic goes as follows; you can fly a plane with one engine, but not without fuel. Propulsion systems would be completely compromised if fuel tanks are taken out.
Internalizing elements is possible (as seen in the tutorial videos) since voxels can be temporarily moved, but having to move them after every few flights seems very inconvenient. Then there is always internalizing most of the tank but having a "window" that exposes part of the tank, but that still has the vulnerabilities associated with an exposed fuel tank.