I've got a 53 plate vauxhall combo, that was used by the post office and then scuba diving in the UK (very cold and dark), so, I've got an excellent cd player with ipod attachments, upgraded speakers and (very essex) a 1000watt sub (not the underwater type)in the rear.
No room for plumbing stuff but it sounds good.
Seriously though, I wish it were slightly bigger, its already full.