David is right about that. Be very careful when sanding between coats, as when you put enough pressure on areas between ribs, longerons, etc. you run the risk of sanding through the material over "hard" areas. Don't ask how I know

I did this on a section of my L-4 fuse, my first Koverall job. Since I wanted it to look like a "veteran" warbird, I figured a couple of patches wouldn't look out of place. "Unfortunately", I didn't account for how well Koverall patches disappear into the finish, and you can hardly see them.