I wouldnt worry too much about the rear end, considering its use and necessary access.
The blunt front end shouldnt be too much of a problem if the corners are rounded enough, and they look reasonable. the truck is so long it should reattach anyways, but still youll want the least amount of separation.
First i would add a fairing on top to ensure flow transistions smoothly to the top and minimizes separation on the roof.
Then i would add skirts similar to those being installed on most bigrigs, coverage to the rear as depicted would be best.
Airdam at the bottom of the nose should help considerably as well, doesnt need to be real low, just enough to get the air flowing down the side of the newly installed skirts instead of the very dirty bottom.
Last i would try to close the gap between the cab and box. should be easy since the truck is all one piece.
