[Sven7]

Still way too steep of an angle at the rear. Can you insert canvas images into Sketchup to build over? If so, do that. If not, overlay the aero template from last page until it matches. Print them out if need be. I posted that image because it's pretty close to the "perfect" low drag vehicle shape. Any steeper an angle will detach the airflow, resulting in eddies and vortexes.

I don't know how to build in Sketchup or convert from Alias, if it's even possible. The best way to do it would be building over an image. Also, if you're making it 4x4x10, define those dimensions in the model! My model is built almost exactly to those dimensions and you can see how much longer it is than either A or B. (That is, unless 4' is measured from the axle up)

If you only make a curve in one direction I'd do A because it will have a smaller frontal area in crosswinds.

Edit: As far as accommodations go, you should be able to fit a bed in there with a little space to walk around, especially if you cantilever the body over the wheels for an extra 10 inches or so.