This is a thread I started when I found an idea on instructables about taking the stock plastic wheel covers stretching a piece of fabric over them and using an epoxy if I remember right to harden them. There is a link to the page with full instructions in that thread but if you find he smoothest covers you can the it should give you a pretty flat surface and there's not a huge chance of them going anywhere.
Here is the link
http://ecomodder.com/forum/showthrea...dea-28207.html