Will be hard to get a thermal gradient in a small enclosure like that. I tend to just use the 1200x595 white melamine sheets from bunnings. You only need 4 sheets and they are $13 per sheet. Get bunnings to cut one in half for the sides and you have a 1200x600x595 box for $52.

i was actually thinking that myself, but i will have a play with the heating and see what happens. my idea would be to put about a 15cm strip of ceramic tile with heat cord under the vent, and make another vent along the opposite side near the bottom. so it would constantly draw a gentle amount of fresh air though the cold side. getting some heating supplies this weekend, so i will test it out and see what actually happens in there.