Cool project, KB.
Question: how did you do the animation in post #1?
I agree with the others: radius the transition to the roof at the leading edge. We discussed that in this trailer thread as well - concensus was you could just split some PVC (or equivalent) and affix it at the roof line.
Radius & boat tail the remaining exposed fender, and skirt it as well.
Depending on time, you could also construct tapered fairings aft of the tires as well, eg:
