I have done this before, by modeling the sillouette of an aircraft and extruding it.
Create a separate part file and label it "projected area". Assemble the vehicle and newly created part together(or use current assembly). Perform an edit part command in the assembly, set the sketch plane to be normal to the projection (so your looking at the very front), then trace the silhouette of the vehicle using either "convert entitles", "Offset entities" w/ offset of 0 inches, are even an intersection curve between the faces and the sketch plane. Extrude the sketch to an arbitrary thickness and then measure the surface area of the part. I guess you could do this the same way as an unmerged body then delete body right in the part file,
if you save the as a dxf you can specify the planes you wish to project to, then you can import the dxf and create a surface from the boundry