Well I ended up backing the wing decal with white paint. As for the tail I used a second decal for backing. Testors paper is great for panel lines. Even with two decal layers and a top coat of clear, I was still able to get rivet details using a setter.
Ether method works great, depending on the size of the decal. If the decal is large, you wont be able to get the white decal to lay down without it folding 2342514634342 times on itself. If that is the case you are better off masking off and spraying down a light color over the base paint.