I still use a line-of-sight method to ensure stab is parallel to wing (after you first set wing correctly).

When standing behind the model, center your line of sight by looking at the fuse and making sure you can see equal amounts of the left and right sides of the fuse. Next, slowly move your head vertically up and down until you see the outside tips of the stab just begin to block your view of the wing. The points on the left and right sides of the wing where the view is blocked should be equidistant from the right and left sides of the fuse. If not, tilt stab slightly until all is equal.

This only applies to wings with dihedral. If you truly have a flat wing, then the task is even easier- just line up the edges of the wing and stab visually from the rear.

- George