HA! According to SpaceinMiniature.com 's Space shuttle Book, the Airfix kit has the best ET.
I haven't tried it yet but Rustoleum has just come out with a new spray paint that makes things look like it has a hammered finish. This may or may not owrk depending on how it looks in scale. But it may be worth a try...
http://www.rustoleum.com/product.asp?frm_product_id=21&SBL=1
Lets hope for a smooth flight