Have you thought about fitting a car sunroof? You could use velcro to fit the mossie net.
I have seen some in breakers yards that were only half size as they had one each side of the car, (think it was a Volvo) I fitted a normal sunroof to my Defender, and there is something really satisfying about cutting a whopping great hole in your roof :funmeteryes: As long as you can seal round them nicely, they would do exactly what you want. There is usually enough room under a roofrack for them to be opened as usual.
Gaz

Nicro ventilators see page 80++. It's a pdf catalog, it can be saved.
http://www.marinco.com/files/media/c...%20catalog.pdf

Dometic roof lights and hatches.
Dometic

My fridge have a shroud around it which is ventilated through the Nicro solar vent Day & Night 2000, the hot air from the fridge passes over the surface of a stainless steel water container on the way out and heats the water in it, the water is used in a pump-up shower.

http://i191.photobucket.com/albums/z...o_4010_4WD.jpg