Wow... I really don't understand any of this.
But yeah, I don't want to get too complicated in my measurements... Mostly what I'm trying to achieve is a chart showcasing power requirements at increasing speeds and increasing, but otherwise simplistic inclines, to show hill-climbing requirements. I'll just add a fudge factor to over-calculate for real world conditions. Wind, temperature and other errata are off my checklist as this is basically designed to scale the battery pack (did I mention this is a pipe dream of mine, an all electric RV?), to a reasonable usefulness.
Now how does a modern bus manage a Cd of around 0.20? Being that it's for all intents and purposes a brick wall, I find that a bit difficult to swallow. Even the newer "chrome dome" style buses seem like they would have massive frontal drag.