After sanding the third coat, I filled a 6 little holes with quick set "aero dynamic smoothing compound" :) and sanded it when cured. I also drilled a 1/16th hole in the manufactured hard spot where the overhead front seat belts will be anchored so I could locate the hard spots later. I then filled the recess around the hard spots with the smoothing compound. I spent quite a few hours sanding and filling the aft roof section even though it will all be covered with a headliner...but I plan to do my phase one fly off without it so it will still look good. When it was all cured, I gave it all one more coat and sanded with 800. The bad thing about Poly Fill is that you need to wait a week before you prime it. Being water based, it needs time to dry up. I plan to prep the edges of the doors next so they can be primed and painted when it is when I do the cabin cover interior.