I had louvers on the back and sides of my mustang and the visibility was a little diminished but not terrible. The thing that sucked was the rattle at highway speeds. As far as radio, wouldnt plastic be ok?

I googled and emailed the people at spoilers for less asking them about the possibility of creating rear louvers out of ABS plastic

http://spoilers4less.com/autolouvers...FUmo4AodLhZLZQ

there are many companies that come up on a search