Fantastic James. The PWM stuff coming out of HK is now so cheap and prebuilt and this one does up to 8A. Your ebay find will probably be a chopper style which is still fine for heaters.
I also found on ebay some buck switching regulators that have a variable output voltage down to just a few volts. Similar price and great for running things like my DSLR at the correct DC voltage (8V), guider (6V) etc. My aim is run everything off 12V.
Thanks for your effort and pointing us in this direction. I will now be revisiting my power box!!
Cheers,
Darrin...