Making the "hole" template
Okay first, I made a simple cylinder approximately the size of the hole depicted in the 3-view drawing. I made sure to have enough vertical segments on the cylinder to make the boolean operations easier later on.
Cutting the hole on the fuselage
To make the illustrations easier to follow, I deactivated the object mirroring function for the fuselage. This will prevent Metaseq from "drawing" the other half of the fuselage object.
Nope... I'll have to ditch the subtraction operation.
Instead, I'll use the intersect operation (Fuselage # Cylinder).