Come here to TX and get some of this Andro stuff. It takes the fire ants right out. (and they come back in 2 weeks so you can kill more )

I avoid putting a seam ON the center of the LE. I feel its asking for the covering to lift and blow the wing open. if you do it... add a layer of clear over the leading edge to move the seam edge back an inch or so.

Cover the bottom of the wing, wrapping to the top of the LE stock at least 1/4 inch back from were your seam will be.

If its not a tapered wing... place the wing on a flat surface. Block the trailing edge up so the wing is level. (0 AOA compared to the tabletop)

Select a piece of 1X2 or other material that comes up to the centerline of the LE. (you should have the idea now) use that stock as a guide to draw a line on the LE with a water based felt pen (Vis-A-Vis markers for overhead projectors are GREAT)

How to cut off the covering and get that straight line... PRACTICE.