Aero D;
Here is how made my wheel covers:
I transfered the rough outline of the wheel coves onto 1/16" thick ply wood and cut it out. Then I fiberglassed over a half of plastic tubing with approx. 1" diameter and ca. 5" in length. After curing of the fiberglass it yielded those half round walls which form the outside of the wheel covers. I epoxied them onto the ply wood and sanded them smooth after the glue had cured. I'll post a few more pictures close up showing the inside of the covers, so you get a better idea. I did spent quite some time fabricating those covers, but I think it was worth the effort.