Here's my own design for a belly tanker (it's not quite as far along as yours
)
The fourth wheel is to qualify as a four-wheel vehicle and could be deleted. The third wheel is semi-enclosed. The front wheels are hubless or wire wheels with flat carbon-fiber spokes.
The body is formless construction, from flat sheets, using pie-cuts along very strategically located lines (along the triangular, diamond or hex outlines).
The shape has octahedral symmetry and approximates an asymmetrical prolate spheroid to more accuracy than your cutting tools.