The best way to measure wing area - that is the most accurate way to find lifting area on virtually any airplane, is to include the area that passes thru the fuselage. It does not matter that there is no wing-shapped cross section there.

The plain fact is - wings create a low-pressure zone above them. This low pressure zone overlaps onto the fuselage with an intensity amazingly close to the pressure value that would exist if there were just a plain wing there. It is generally within a 10% difference. This can be verified by wind tunnel tests, flight tests, or just comparing computations based on wing area to actual performance

When figuring total wing lift, a difference from perfect wing lift of 10% over say 10% of the wing area( the part "in the fuselage") results in a total lift difference from actual lift of 1% (10% x 10% = 1%).

Compare this to ignoring the wing area "in the fuselage" You ignore all the lift that is really there (90% of lift a wing "would" give". Thats a 9% difference in lift from what a plain wing would do(90% x 10% = 9%).

When evaluating a plane - a 1% difference can be ignored for initial evaluation, a 9% difference you ignore at much greater risk - and error. The method that outcast gives is neither the most common or the most accurate. Anyone who designs airplanes seriously - from BVM to Boeing - understands this.

Anymore of this should be taken over to the aero forum.