As I understand it, nitrate is not fuel proof! However, it's cheaper and lighter than butrate, so it's good to use to fill the weave of the fabric after it's been applied. Then you can put butrate over the nitrate to get a nice, fuel-proof, finish. I think that you can't put nitrate over butrate (not that you'd want to) because it'll craze up.

I have done several planes with Koverall, and to me, Stix-It is the only way to go. Put a coat or two of Stix-It on the edges of where your covering panels will be, then after it dries, put the Koverall on with your sealing iron. The Stix-It grabs the covering and holds it solidly. When you heat-shrink the covering, it won't pull away.

The first plane I covered with Koverall I used only dope to attach the covering, and it was a major pain getting it to stick, especially to compound curves.

Phil