I've recently looked into SPAD airplanes also. They look realy neat, and for the price your can't beat em. Since it's coroplast, pretty much advertisement stands, I would just use a marker or paint on it. I don't know if Monokote would stick to Coroplast, but it doesn't hurt to try. Which model are you going to build? There are so many to choose from.

Sorry if I wasn't much help.

-Brian