The bottom edges of the plastic caps are not exactly even or straight so I found a flat board and taped some 60 grit sandpaper to it. This allowed me so run the pieces back and forth until the edges were straight and level. The cap was then placed, holes drilled one at a time, then clecoed before the next hole was drilled and the plastic wraps around the contour the alumium shape.
After instalation, the gap was checked to make sure the overhand of the vertical stabilizer wouldn't impede the rudder at full throw. I'm not sure, a little rub may be possible, so I'll have to gig up the stab and rudder to make absolutely sure before paint. Otherwise I'm very happy with the results!
