I'm thinking 10" wide openings.

Glad there's lots of interest. It'll help amortize the tooling costs. I could design them in CAD and do CFD except I'd really need CAD of the car itself. I have a CAD model of the car, but it's an estimation. As for CFD, mechanical engineers split into two main groups halfway through school. There's the solids/vibrations/controls guys and then there's the fluids/thermo guys. I have access to CFD software, but it's garbage in garbage out. I could probably get some data, but without a full car model it's pointless. The computing power required to do that would be quite intensive too.