Any clear dope, even nitrate will take 8 to 12 coats to fill light weitht silk, and Koverall is much thicker. However, with a color coat it may take as little as two coats. Light weight silk is easier to fill than medium weight silk span, but it takes more than light weight silk span. Typical stunt paint procedure for medium silkspan is, two to three coats of clear nitrate dope, one or two coats of acrilic auto primers, sand lightly, three coats of silver butyrate dope or two coats of silver acrilic laquer, sand until primer shows and recoat with silver repeat untill glossy smooth, three to six coats of color butyrate dope or one or two coats of acrilic laquer sanding with 600 or higher grit between each coat. I don't recommend using butyrate dope because you have to wait a week to sand without gumming up your sandpaper. If using laquer (or even dope) add some plastisizer to it or it will harden and crack in a few years unless you coat it with restoration solvent every year or two.

Obviously this is a lot of work! And with drying time of a week between sanding it will take several months! The competition stunt guys do this because they get 20 points for apperance, if they use the same plane the next year the points are reduced. While they are flying this season's competition on weekends, they are working on next season's plane. So longivity is not an issue.

Reccommend that you spay a coat or two of automotive lacquer, and finish with polyurethane or automotive paint. Actually the giant scale guys would probably know how best to fill the Koverall.