I have one of these
Bose Wireless Speakers | SoundLink Mini II Special Edition mounted in my front overhead tray, secured by 3M heavy duty velcro. It does not move or bounce around and you cannot see it unless you get your head up there to look into the tray. I bought a 10 foot USB cord and ran it down the front pillar and into the glove box where I wired a USB plug. Sound quality is excellent and since it's plugged in it charges when the cart is turned on. Best part is that I can simply just detach the velcro and bring it with me if I need to.