I began by tracing out the top and sides of the tank, this will have a 1 piece bottom tunnel, and 5 piece top (top, left, right and 2 knee wells). I started with the top, and using a mallet and dolly, and the wheel, I formed a strip to match the contour of the tank model, I did the right side the same way, getting the rough shape out with a mallet and shotbag, then the smoothing is done on the wheel. The progress pics are what I took shaping the left side, same process, going back and forth between the wheel and the hammers too, since there's quite a bit of crown in the piece. The tunnel is one piece, and will help to keep things stable once I start tacking pieces together.