For a channel-wing design, get a big-diameter PVC coupler or something like that and cut it in half. You can easily cut it with a hacksaw and shape it with sandpaper... unfortunately, the dust is pretty toxic, and the glue is very nasty, too. If you go with this material, do it outside... ditto for blue foam or similar; toxic dust and very nasty fumes when cut with a hot-wire knife(cyanide, anyone?)
Linotube (heavy-duty cardboard tube) would work well, too, and it's safer,but it's harder to shape.
good luck...and don't put an eye out!
