I also have the stereo installed w. outdoor speakers under the stern arch. But they are 8 ohm impedance and not as loud as the 4 ohm car type in the cabin. Still nice to have tunes inside and out - and not have to worry about kicking the cord of the boom box out of the power bar all the time.
Solar panels added to the stern arch. 375 watts of 'em. Woo hoo. That should run a fan or two.