dr_wogz has it right....ellipses are the way to go. You NEED to get yourself a CAD program and spend the time to learn the basics. You'll never look back! If you don't have one, there are free downloads of TurboCAD that are excellent.

The 1st photo below shows the rear section of an autogyro that I drew up in T/CAD which has half-elliptical rear fuse bulkheads. Once you're happy with your side and top view fuse contours, you draw ellipses at the necessary stations with the major and minor radii matching the appropriate height and width.

The second plane was designed exactly the same way. How did we get along before CAD??