There is a program Hull Designer that is used to design boat hulls built out of flat plywood panels. It could also be used to design fairings made of coroplast.
Carlson Design Plotter/Cutters
Here is a short wheelbase recumbent bicycle fairing I designed using this software. The output is this image, plus dxf CAD files with coordinates to mark the coroplast sheets so you can cut out panels.
This fairing is just an example of the output of the program. It looks odd because the bike is so short and it has a high handlebar, so space is needed on top. You need to picture the riders head sticking out above this fairing.
I realize that flat panels are not as aerodynamic as rounded, however this type of fairing would be very easy to build and pretty cheap as well. The software would allow more than just two panels to the side, you can choose any number of panels. I was thinking of zip tying the panels together, then covering the joints with clear packing tape. I would design the fairing about 6" longer than it had to be, then cut it in half behind the rider, and use a hinge at the very front to raise the front half up, and when the front half is down it would overlap 6" over the rear half.
I have used this program to build canoes and small boats, it is very accurate and you definitely get the shape you design. It takes a while to get used to, and it would be worthwhile to build a few models. I usually take the output in dxf format and open it with Autocad, and then draw a 1' x 1' grid on it and take the coordinates of the upper line and lower line of the panels every one foot. Draw the outline using a long bendable straightedge, cut the panels out and stitch them together.
Here are some boatbuilding outputs from Hull Designer:
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