I built the first one you suggested Larry and mounted it to a CPU heat
sink from an old junk computer I had. I hadn't checked back here to see
the larger units that you fine folks suggested at the time. It got
plenty warm. Not too hot to touch, but still plenty warm, so I took the
12V fan that was mounted to the CPU heat sink and mounted it too. Put
the set-up in an old small unamplified computer speaker enclosure with
the grill from the other speaker mounted along a cutout I made on the
backside for flow-thru ventilation. I even went for some bells and
whistles. I mounted a 140° thermal switch with a light bulb to the
heat sink.
Everything works great! The air flowing out of the regulator enclosure
is not noticeably warm at all. Cooler than the air flowing out of the
inverter when I was using it for the same MP3 player. So I'd say I'm
ahead efficiency wise.
Even starting out with the MP3s battery fully charged it still must draw
quite a bit of current. It's a old 20 gig player that has an actual
hard drive as opposed to flash memory.
I'm going to check the current draw the next time I use it just out of
curiosity. The 140° indicator light hasn't came on yet.
I kept notes on the sites you all posted for the larger regulators in
case this one ever smokes. Thanks again for your help everyone.