How about MP3 loaded cds ?
I have a little black jewel case ( like a ladies compact ) that holds only 2 discs. It disappears above the sunvisor.
Never counted the total tunes, more than enough for me.
I do have a USB port in the glovebox. Its only been used for phone charging and a little snake light.
By the way.. I found the cast and chromed brackets available for Bazooka base cannon seem to suit the cars appearence very well. A touch of chrome in the trunk :)