What you can do for the "flexiible neon" is use one of two things. They make this EL wire, which is wire that glows. Not too many colors available, the basics, blue, green, red.
http://www.xoxide.com/elwire.html
if you want good and cheap neon, cathodes and other stuff, check computer modding webistes, since the computers run off ofthe same 12v. The computer mods can work with the car!!
the other thing you can do is actually bend the cathodes. What you do is use a candle or controlled flame to heat up the tube (make sure you take it OUT of the plastic tubing before hand) and slowly heat it up. WARNING IT IS GLASS! IT WILL BREAK ON YOU! so once you heat it up, you slowly start to bend it to the shape you want. Then you just install it. Be careful though, since they can break. Cant find the website right now though.