Andrew basically the way I do it is that I cut two strips of the plastic covering material about 1" wide and however long the width of the roll is. So what you end up with is two strips of covering that you will lay next to each other with the adhesive side up on one of the strips and the adhesive side Down on the other strip. Overlap the edges of the strips by about 1/8" and CAREFULLY use a heating iron set on low heat and fuse the two strips together on that 1/8" overlap. Then cut the hinges cross ways the width you prefer and you will have your hinges. Then you just Iron them on the moveable part (flap or elevator) in alternating one on bottom and one on top, one on bottom, one on top . Once you have your hinges attached on your moveable surface then you can fit them to the stab or trailing edge of the wing and iron them down on those surfaces.
Walter Umland used to have a pictorial step by step of what I just explained but his web site says it is down because he has been sick....maybe someone on here has a copy of it....
Hope this helps
Mike