I started fitting the LH upper flap skin by sanding a chamfer into the bottom of the top skin to clear the flap leading edge cuff. I used a 3 inch sanding disc to get the bulk of the material off. I finished up with a permagrit sanding block. I then installed the flap lower skin onto the wing and started sanding the shear web. Lots of trial, sand a little, trial, etc. I have the flap upper skin fitting pretty well but I will double check it tomorrow before committing that it is done!