Whenever you have a double contour you will have to cover in sections. You're right you can put butyrate over nitrate but not the other way around. If you will be covering with tissue you can shrink it with water and then paint it. If these will be non-flying why not investigate Testors. You are probably familiar with it if you have built plastic models. Wide range of color choices and scale military colors as well. Look to Major decals for markings. Doping the tissue for non-flyingmodels is usually not necessary. Sig sells nitrate. You can thin it with Acetone. Butyrate requires a different thinner. Are you going to spray or brush? That will make a difference too. Testors comes in small spray cans or bottles for brushing or air brushing.