We've been running some super cheap thing from wal-mart and it has been amazing. 3 years and counting and it still runs. It was like a $40 "DUAL" head unit... doesn't even play CDs but has the following:
SD card slot
.... so we are able to run anyone's mp3 player/cell phone for music, charge, and I just keep a 8 gb sd card in there as a backup.... best part is, that if it gets trashed we really don't care, we'll just buy another.
EDIT: We have a Nautique Supersport so I assume the mounting is the similar if not the same