Super Coverite
Sig Koverall is similar to Coverite, except you dope it on, and then need several coats of dope to fill the weave. But for sheeted wings as you mentioned, .6 oz. glass cloth is hard to beat, applied with the Pacer Laminating Resin, or with nitrate dope. A second option is silkspan and nitrate dope....gives a nice flat hard finish ready for primer at a minimum of cost.
Clair Sieverling