What makes these units so unique is the electric opening of the vent itself. Just so kooool! But that's not all, as if it starts to rain a small sensor activates the closing mechanism. This is wonderful for those of us travelling with pets. If you pop off into a National Park and have to leave pooch inside the A'van and it rains it will close automatically. As soon as it stops and the sensor dries off it automatically opens once again. You can see this mechanism in the bottom right of the photo on the left below. All it consists of is a small piece of printed circuit board with two squiggly lines. As soon as water bridges at any point the vent closes. We loved the way the fan automatically switches off just before it closes fully - totally idiot proof. It also has a high volume REVERSIBLE fan with a thermostat. You can set it to switch on if the temperature inside your A'van rises. There will be fitting instructions in the DIY section in the near future. They are expensive in that they are almost as dear as an air conditioner yet they have none of the high power requirements and will run off a large solar cell or even the small one if you use the lower speed. The info below is from Fantastic's website. The site is a little slow to come in as there is a Flash demo of the vent opening automatically - well worth watching though if you haven't seen one in action. The company by the way trades as Fantastic Vent if you happen to forget the internet address and resort to a search engine. You can buy them in Australia from Camec, and yes you can get the nifty smoked cover to match your existing vents. Special thanks to Adohen Supply Co (USA) for the excellent photos used on this page.

This is the top of the range model and the one we are about to install. Select speed (1-low, 2-medium or 3-high). Placing the IN/OUT switch in the centre (neutral) position can turn off fan blade.
Automatic Dome Opener with Built-In Rain Sensor
This model is activated when the three-speed switch is turned to any of the three speed selections. The dome cover is opened when the dome up switch is activated and closed when the down feature of the switch is selected. To activate the fan blade, the built-in thermostat must be turned to a temperature selection, which is lower (cooler) than the current interior temperature. Once the selected temperature is attained, the fan blade will shut off, but the dome will remain open until the down feature is selected or the built-in rain sensor becomes wet. Once the sensor dries, the dome will re-open. A built-in manual knob can be used to close the dome in an emergency, to adjust the dome to a desired partially open level or to override the rain sensor. For storage, the dome switch must be in the down position and the three-speed switch in the off ("O") position.

http://www.fantasticvent.com/How_To_Install.html

"Definitely a great addition to any rig... a "Fantastic Fan". This is a high volume 12 Volt fan that replaces one of your existing roof vents. It draws very little current and can really help keep the rig cool without using the A/C. On low, it only draws a couple of amps and on high, it will exchange the air in your rig for cooler outside air in a minute or two. Find them at any camping retailer  ...Adohen Supply Co. " Scott from Adohen Supply advised us by email (December 2004) that he can land the top 6000 model in Australia for AU$419.00. This is a very keen price as Aussie price are $500 and above.  Mark's website Interesting 12 volt how to do stuff! 

Another good page illustrating ease of installation even though it is on a motorhome - the principles are exactly the same EXCEPT you need a special kit to install in thinner roofs. 

http://www.motorhomereviewonline.com/fantastic_fan.html