The slope at the seat end of the tank seems to be at the reverse angle from normal, and while you may be doing that on purpose to be different, I recommend moving the slope back to the more conventional angle as that angle will be more comfortable for a crouched riding position which will lead to better control and more time spent in the seat! I also feel it would look better too. The rest of the tank has a very natural shape that seems to flow with the frame well, also seeing the outline of the top axis will help visualize your final shape. How do you plan on building your tank? Material, methods, tools used?