Page 14 Modeling a Tank: Body Detail

Hide the body.

Extrude the curve shown above and drag the extrusion to a distance shown below.

From the right side view select the Extrude object and drag to the left as shown below.

Rotate the surface clockwise to align it to the projected side curves (it's about a 20-degree rotation).

With the object still selected, Copy 'Inplace' 2 times which will give us a total of 3 objects to BooleanDifference away.

BooleanDifference the red objects from the Extruded side objects as shown in progress below.

Turn off the 'side bool curves' layer and hit Show to unhide the body.