I actually bought a hidden antenna for the cuda but never hooked up a radio. Cant remember where I bought it. Come to think of it, i'm not even sure where the heck it is.
anyhow, it was basically a wire that had a backing tape so you could stick it on your windshield or rear window. It ran the length of the window and if you tucked it up real high and tight you probably wouldnt be able to see it.
They are out there. search around