I had intended to stay out of this. There is an easy way. This may or may not apply to the predator. In the side view of my airplanes the elevator hinge line is 90deg to the wing chord line. I designed it that way for a purpose. There are four axes to set.

So with the wing mounted to the fuselage turn it upside down. Block up the wing so the incidence is correct and the tail seat is just resting lightly on the upside down vee tail. Axis one is now set.

Centre the tail in the fuselage. Axis two is now set

Stand a square against the wing T.E. Moving the square along the T.E. as you do it measure from the square all along the hinge line both sides. When it measures the same along both hinge lines axes three and the incidence are set.

Set it up roughly before applying glue.

Ed S