Hi Starwolf,
I'm glad you got that doubler figured out. I knew you could do it. Nice work.
Make sure that you sand that leading edge to match the plans and keep it straight along it's lenght. If you use a 2 foot long sanding block this becomes an easy task. When you are attaching sheeting it is important to keep the wing half that you are working on tight to your building board. Pin it tight in areas that will allow you to remove the pins later. You don't need the plans underneath it. If it's not flat and straight it's likely you will end up with a warped wing, and warped wings do not fly well. Pin it down so you can cover the top of the wing first. After the top sheet is on it is less likely to twist.
I like using contact cement (Weldwood) because it is the easiest method and holds on like grim death. Coat the framework wherever the sheeting will touch, and the underside of the sheeting with a thin coat. Let it dry to the touch. Line up the sheet. Use pins to slide it down and guide it into place. You only get one shot. You cannot move the sheeting after it is down. When the top is covered you will find that the wing structure is becoming more ridgid and it is easier to keep it flat and straight. Use the same method on the bottom. You may have to elevate your board to allow for the dehydral in the wing when it is upside down.
Good Luck