I wouldn’t do that. Anything you do to your VHF has potential to degrade its performance, and your VHF may well be your most valuable piece of safety equipment someday.
I find that music in the helm area distracting when trying to listen to the VHF traffic.
IF you insist on having speakers outside the boat, install an ON OFF switch and also a separated volume control. Others around you may not appreciate your music. MUMBLE MUMBLE.
I have a small wire type antenna made for a boat which I just have run inside the flybridge. works fine. As has been said, don't try to use the VHF antenna.
I really get a kick out of boat listings where the owner spends more time describing the sound system than the mechanics or maintenance of the boat. Sometimes showing pictures of the speakers, etc.
Same goes for the underwater lights.
Both are often on "Go Fast " boats or wakeboard boats. To each his own, I guess.