Some great ideas in here. I have a Donjoy Iceman cold therapy box that'd be great for this if it ran on 12v instead of 7v. It works awesomely for a sprain or to quickly recover from extreme heat. It's temp adjustable with an inline thermometer and a bypass valve. I guess I could try it on my regulated power supply and watch amperage as i turned voltage up...interesting. On the other hand a 12v in, ~7v supply shouldn't be hard to come up with.
This buck converter says it's over 90% efficient and they're usually pretty durable, for $9, what's to lose?