Last week I applied two coats of body filler to the front apron, sanding in-between. After the last coat the surface was rough, so I did a little sanding to straighten it out.
I applied some black guidecoat and sanded again to reveal the high and low spots.
And I also used the guidecoat on the top surface of the apron.
So I continued sanding to bring down the high areas to the level of the lows, creating a uniform surface.