Kammback vs spoiler-or both?

[BamZipPow]

Best way to cut Coroplast is a knife/razor. If yer doing a straight cut, use a straight edge and only penetrate the first layer. You can then fold it back and cut from there.

If yer doing a curve, just take yer time. You might git better results by making several passes on the cut.

[freebeard]

I was going to suggest a knife blade or a fine-tooth blade in a reciprocating saw.

Coroplast is popular here, but it is impermanent. Consider PolyMetal or Alumipanel or Omega-Lite. They're all plastic sheets, typically 3mm thick, with enamelled aluminum skins on both sides. Their light as coroplast and as stiff as plywood, weatherproof and can be sheared, rolled and braked by hand (given a floor mounted shear/roller/brake with an adequate throat).

I buy scrap at the local hippy recyclers. They also have polyurethane formed like coroplast.