[aerohead]

Naked, without the tow vehicle in front, approx. Cd 0.90.
A frontal area is necessary to begin any numbers-crunching. Measure everything.
She'll have to investigated as a 'system' as well, so we need all we can get for the tow vehicle as well.
AeroStealth's F-150 / Cougar Fifth-wheel is indicating around Cd 0.26 as a 'system, @ 100 Square-feet frontal area. 9.5-mpg @ 100 km/h.
I hope you know someone with an industrial-grade sewing machine, or an awning company.
An extremely light, aluminum-framed, stretched-fabric nose and boat-tail could easily be fabricated for such a simple structure, and serve as sun-shade when not mobile.
Awesome project!