I'd be happy to tell you how the fluting was done.
The cars sides (masters, if you want) are made up by glueing Evergreen plastic material onto a piece of .060 thick black base material by Plastruk (interesting in light of the 'ABS to styrene' debate going on elsewhere, and I use Testors glue; no problem). I don't think it's possible to construct a car side without the base; the base provides a stable platform to build up the side on, and there are lot of little pieces of white plastic involved!
The first strip is a piece of .020 x .030 glued to the base on its edge, such that the .020 side is glued to the base. It's vital that this piece is perfectly straight; use a steel ruler. Let the glue set thoroughly. This is the belt rail under the windows. Next add a strip of .020 x .020 under the belt rail, using moderate pressure to make sure this strip is pressed up against the belt rail AND securely down onto the base. I've noticed that some Evergreen strip material as a very fine texture that looks like 'saw marks' on one or two sides of the strips so I try to avoid having this texture visible on the finished surface. The next strip is a length of .010 x .030 placed on edge to form the first of the raised corregations, carefully pressed up to the last strip and down to the base etc...
Repeat as required (7 times in this example). I did 2 or 3 strips and then paused to let the glue set before adding more. I also let the the strips run a little long as I applied them and cleaned them up to the correct length after the glue set. I used a piece of .060 x .030 for the car name plate and the final strip is another piece of .020 x .030. Then I used some extra fine modeller's sandpaper to polish up the top surface and smooth out any inconsistencies. Once the fluted panel was complete, the rest of the car side was built up around it.
Obviously this method does not result a fluting with curved concave or convex surfaces, but it still seems to work. The fluting applied to this particular car was in reality quite 'square' so this method provides a more prototypical result than you might think.
Final thought: you could try to build up the the fluted panel on a base of .010 thick plastic and the cut this free to allow for a more typical car building strategy, but I think you would have go slower and be careful to keep the glue application as light as possible to avoid warping the panel.
Geoff