Finally decided to put a Radio in... and what a job.
4 speakers in the rear two next to the rear doors and two by the back - well above the "water line". Cables run out and underneath (nearly 34mtrs!). Aerial fitted using an existing hole, radio in an under dash case.
Took a long time to get right. Previously I'd installed oil and temp gauges and added a volt meter too this time. Just need to wire up the lighter so I can charge the moby and run a sat nav.