Hi
Some photos attached.
I used ~12 x 2.2ohm, 2 watt resistors. On mains, I connect to the same supply as the scope, in the field I have a seperate battery, 12V, ~7Ahr.
I suggest having a look at this link,
http://www.iceinspace.com.au/63-292-0-0-1-0.html, I think I based mine on this.
Philip
PS try the fan, at home, it should be easy enough.