For rough drag calculations I made three bounding sketches in three planes and made flat surface from them. Next you can mesure area of this plane surfaces.

For more accurate calculations I get data about orientation of each member of my structure (coordinates of three points: origin, point on longitudinal axis and point on transverse axis, third axis you get by cros product of x and y). These three normalized vectors give you Rotation tensor of member CS, after this you can find drag and lift forces on each member.