Smitty: I so LOVE that tin ceiling idea. Super cool.
Heidi: I'm fairly certain I, too, have seen others use the Luan on the ceiling. Unfortunately, I know nothing of how it would work long term.
We painted our ceiling with two coats of ceramic additive http://www.hytechceramics.com/insulatingadditive.html
for insulation purposes. Then we painted a sky over the top of it. Day sky at the front of the bus fading into a night sky at the back. Not finished with it yet but there will soon be a sun at the front and a moon in the back. And maybe some little LED stars (lights)?