RE: Making large sheets of balsa help please
What's wrong with simply using a straight edge to get nice edges on each piece and gluing together with wood glue? A doubler isn't needed.
Do it over wax paper, press together, squeegee out the excess, tape together with masking tape, and weigh down (with another piece of wax paper on top) until dry.
This is how I make very large skin sheets out of 36 x 3 sheets. Note when making really large sheets to stagger the joints (kind of like laying a hardwood floor). Also, the long edges of the individual pieces should ideally be perpendicular with whatever curve you may be laying over.