Jack,
I don't know just how "clean sheet" you want to go with this project, but it just seems to me that the pontoon fender style body is always going to be inherently "dirty" from an airflow standpoint.
To look to history for an example of a "clean" body shape that would also be easy to construct, how about the Bugatti Type 32 Tank?
http://www.acmenovelties.net/cars/20...pe_32_tank.jpg
That shape could be built fairly easily using big box store foam insulation board covered with fiberglass. Add a Kamm-back top and full wheel skirts and you could have a very clean and light cover for your running gear in short order.
You might wind up with something that looks like it escaped from the prop room of the Buck Rodgers serials, but I for one don't think that's a bad thing!
I love your project -- keep up the good work!