G'day Kearn, You can get to the same result if you carefully equalize the temperature of your mirror so that it's equal to the surrounding air, and use something like unpainted aluminium for your tube. This combination will stop tube currents.
I cool my primary with an active refrigerating-thingy made from a couple of peltier coolers and some old heatsinks and fans, and it does the job nicely. The cooling unit also closes off the mirror-end of my tube, so that makes it even harder for air to circuate into the tube from outside.
I've written a few short articles about this cooling on my website,
http://www.acquerra.com.au/astro/
regards. Bird