Myself and some others have the MAS racing one for Cudas. The Challenger one basically looks the same. It's just a thin fiberglass spoiler and doesn't come with any mounting holes or hardware (what do you expect for 50 bucks)
I used the drain holes on the front valance and drilled through the 90 degree lip on the spoiler. I like the way it looks. I'll eventually makes some brackets and fiberglass them in to the back side of the spoiler to better support the bottom.
I know it's not a Challenger, but it at least gives you some idea of how it looks.
There's this TransAm style one that's really long for Cuda's. Perhaps this would fit a Challenger or there's a Challenger version floating around?
http://transamcuda.com/spoilers.htmTravis
72 Cuda