I have had really good luck the with the Thunder AC-6, here is youtube link to a demo.
http://www.youtube.com/watch?v=pQIancXVHV8
It is a Chinese knockoff and I have been giving it a workout for over a year without any problems. Since the price right I actually bought 2 of them. Check out the attached photos that show how I installed them on a ammo can. I wanted to be prepared to close and lock the lid in case of a fire. The AC or DC power option allowed me to connect the power cables to one AC cord.
They are going for $55 at
http://www.hobbypartz.com/thac6smbachw.html